Beam shaping for ultra-small vertical cavity surface emitting laser (vcsel) arrays

ABSTRACT

A laser array includes a plurality of laser diodes arranged and electrically connected to one another on a surface of a non-native substrate. Respective laser diodes of the plurality of laser diodes have different orientations relative to one another on the surface of the non-native substrate. The respective laser diodes are configured to provide coherent light emission in different directions, and the laser array is configured to emit an incoherent output beam comprising the coherent light emission from the respective laser diodes. The output beam may include incoherent light having a non-uniform intensity distribution over a field of view of the laser array. Related devices and fabrication methods are also discussed.

CLAIM OF PRIORITY

This application is a continuation application of and claims priorityfrom U.S. patent application Ser. No. 15/951,760 filed Apr. 12, 2018,which claims priority from U.S. Provisional Patent Application No.62/484,701 entitled “LIGHT DETECTION AND RANGING (LIDAR) DEVICES ANDMETHODS OF FABRICATING THE SAME” filed Apr. 12, 2017, and U.S.Provisional Patent Application No. 62/613,985 entitled “ULTRA-SMALLVERTICAL CAVITY SURFACE EMITTING LASER (VCSEL) AND ARRAYS INCORPORATINGTHE SAME” filed Jan. 5, 2018, with the United States Patent andTrademark Office, the disclosures of which are incorporated by referenceherein.

FIELD

The present invention relates to semiconductor-based lasers and relateddevices and methods of operation.

BACKGROUND

Many emerging technologies, such as Internet-of-Things (IoT) andautonomous navigation, may involve detection and measurement of distanceto objects in three-dimensional (3D) space. For example, automobilesthat are capable of autonomous driving may require 3D detection andrecognition for basic operation, as well as to meet safety requirements.3D detection and recognition may also be needed for indoor navigation,for example, by industrial or household robots or toys.

Light based 3D measurements may be superior to radar (low angularaccuracy, bulky) or ultra-sound (very low accuracy) in some instances.For example, a light-based 3D sensor system may include a detector (suchas a photodiode or camera) and a light emitting device (such as a lightemitting diode (LED) or laser diode) as light source, which typicallyemits light outside of the visible wavelength range. A vertical cavitysurface emitting laser (VCSEL) is one type of light emitting device thatmay be used in light-based sensors for measurement of distance andvelocity in 3D space. Arrays of VCSELs may allow for power scaling andcan provide very short pulses at higher power density.

SUMMARY

Some embodiments described herein are directed to a laser diode, such asa VCSEL or other surface-emitting laser diode or edge-emitting laserdiode or other semiconductor laser, and arrays incorporating the same.

In some embodiments, the laser diode may be a surface-emitting laserdiode. The laser diode includes a semiconductor structure comprising ann-type layer, an active region (which may comprise at least one quantumwell layer), and a p-type layer. One of the n-type and p-type layerscomprises a lasing aperture thereon that defines an optical axisoriented perpendicular to a surface of the active region between then-type and p-type layers. The laser diode further includes first andsecond contacts electrically connected to the n-type and p-type layers,respectively. The first and/or second contacts are smaller than thelasing aperture in at least one dimension.

In some embodiments, the laser diode may be an edge-emitting laserdiode. The laser diode includes an n-type layer, an active region, ap-type layer, and first and second contacts electrically connected tothe n-type and p-type layers, respectively. A lasing aperture defines anoptical axis oriented parallel to a surface of the active region betweenthe n-type and p-type layers. The laser diode further includes first andsecond contacts electrically connected to the n-type and p-type layers,respectively. The first and/or second contacts may be smaller than thelasing aperture in at least one dimension.

In some embodiments, a method of fabricating a laser diode, such as aVCSEL or other surface-emitting or edge-emitting laser diode, isprovided. The method may include fabricating an array of discrete laserdiodes, for example, using micro-transfer printing, electrostaticadhesion, and/or other mass transfer techniques.

In some embodiments, an array of discrete laser diodes (also referred toherein as a laser diode array or laser array) is provided. The array oflaser diodes may include surface-emitting laser diodes and/oredge-emitting laser diodes electrically connected in series and/orparallel by thin-film interconnects on non-native rigid and/or flexiblesubstrates. The array of laser diodes may further include one or moredriver transistors and/or devices of other types/materials (e.g. powercapacitors, etc.) integrated in the array.

According to some embodiments, a laser array includes a plurality oflaser diodes arranged and electrically connected to one another on asurface of a non-native substrate. Respective laser diodes of theplurality of laser diodes have different orientations relative to oneanother. The respective laser diodes are configured to provide coherentlight emission in different directions, and the laser array isconfigured to emit an output beam comprising the coherent light emissionfrom the respective laser diodes.

In some embodiments, the output beam may include incoherent light havinga non-uniform intensity distribution over a field of view of the laserarray. For example, the field of view may be about 80 degrees to about180 degrees in some embodiments, or greater than about 150 degrees insome embodiments. In some embodiments, the laser array may be a LIDARarray.

In some embodiments, the non-native substrate may have a curvature thatprovides the different orientations of the respective laser diodes.

In some embodiments, the non-native substrate may be a flexiblesubstrate that is bent to define the curvature.

In some embodiments, the non-uniform intensity distribution may becontrollable responsive to a control signal to alter the curvature ofthe flexible substrate and/or responsive to power supplied to therespective laser diodes, for example, via selective addressing of therespective laser diodes.

In some embodiments, the flexible substrate may be supported by at leastone mandrel element that is configured for movement in one or moredirections responsive to the control signal, where the movement of theat least one mandrel element alters the curvature of the flexiblesubstrate.

In some embodiments, the surface may be a back surface of the non-nativesubstrate, the respective laser diodes may be arranged to provide thecoherent light emission through the non-native substrate, and thenon-native substrate may be formed of a material that is transparent toand is configured to at least partially collimate the coherent lightemission.

In some embodiments, respective features on the surface of thenon-native substrate may provide the different orientations of at leastone of the respective laser diodes. In some embodiments, the respectivefeatures may include unequal-height features and/or recesses that aresized and spaced to provide the different orientations of the respectivelaser diodes. In some embodiments, the respective features may includerespective patterned surfaces of the non-native substrate.

In some embodiments, the laser array may be configured to emit theoutput beam without a refractive optical element on the plurality oflaser diodes.

In some embodiments, a lens array may be attached to the non-nativesubstrate. The lens array may be configured to increase a divergence ofthe output beam in at least one dimension.

In some embodiments, a surface of the non-native substrate opposite thelaser diodes may define the lens array.

In some embodiments, the lens array may be formed of a flexible materialhaving a curvature corresponding to the non-native substrate and/orcorresponding to the different orientations of the respective laserdiodes.

In some embodiments, the lens array may include a primary lens arraythat is configured to increase the divergence of the output beam in afirst direction, and a secondary lens array positioned to receive outputbeam from the primary lens array and increase the divergence thereof ina second direction. For example, the first direction may correspond toan azimuth angle of the output beam, and the second direction maycorrespond to an elevation angle of the output beam.

In some embodiments, the lens array may include at least one of aFresnel lens, a plurality of shaped lenslets, or a plurality of balllenses.

In some embodiments, respective ball lenses of the plurality of balllenses may be suspended over respective subsets of the plurality oflaser diodes. Optical axes of the respective ball lenses may be offsetwith respect to optical axes defined by respective lasing apertures ofthe respective subsets of the plurality of laser diodes.

In some embodiments, a subset of the plurality of laser diodes maydefine a column of the laser array, and the lens array may include acylindrical lens that is aligned with the column.

In some embodiments, the respective laser diodes may include a residualtether portion and/or a relief feature at a periphery thereof.

In some embodiments, a spacing between immediately adjacent laser diodesof the plurality of laser diodes may be less than about 500 micrometers,less than about 200 micrometers, less than about 150 micrometers, lessthan about 100 micrometers, or less than about 50 micrometers, butgreater than about 30 micrometers, greater than about 20 micrometers, orgreater than about 10 micrometers.

In some embodiments, respective subsets of the plurality of laser diodesmay be electrically connected in series (or anode-to-cathode, that is,such that an anode of at least one laser diode of a subset of theplurality is connected to a cathode of an adjacent laser diode of thesubset, or vice versa) on the non-native substrate.

In some embodiments, the respective laser diodes may be surface-emittinglasers, and respective lasing apertures of the surface-emitting lasersmay define optical axes that are oriented in the different directions,respectively. Respective electrical contacts to the surface-emittinglasers may be smaller than the respective lasing apertures thereof in atleast one dimension that is orthogonal to the optical axes.

According to some embodiments, a method of fabricating a laser arrayincludes providing a plurality of laser diodes arranged and electricallyconnected to one another on a surface of a non-native substrate.Respective laser diodes of the plurality of laser diodes have differentorientations relative to one another. The respective laser diodes areconfigured to provide coherent light emission in different directions,and the laser array is configured to emit an output beam comprising thecoherent light emission from the respective laser diodes. In someembodiments, the respective laser diodes may be provided on the surfaceof the non-native substrate using a micro-transfer printing process.

Other devices, apparatus, and/or methods according to some embodimentswill become apparent to one with skill in the art upon review of thefollowing drawings and detailed description. It is intended that allsuch additional embodiments, in addition to any and all combinations ofthe above embodiments, be included within this description, be withinthe scope of the invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example light-based 3D sensor systemin accordance with some embodiments described herein.

FIG. 2A is a plan view illustrating an example laser diode with reducedanode and cathode contact dimensions in accordance with some embodimentsdescribed herein.

FIG. 2B is a cross-sectional view of the laser diode of FIG. 2A.

FIG. 2C is a perspective view illustrating an example laser diode inaccordance with some embodiments described herein in comparison to aconventional VCSEL chip.

FIG. 3A is a perspective view illustrating a distributed emitter arrayincluding laser diodes in accordance with some embodiments describedherein.

FIG. 3B is a perspective view illustrating a distributed emitter arrayincluding laser diodes on a curved substrate in accordance with someembodiments described herein.

FIGS. 4A-4F are perspective views illustrating an example fabricationprocess for laser diodes in accordance with some embodiments describedherein.

FIGS. 4A′-4G′ are cross-sectional views illustrating an examplefabrication process for laser diodes in accordance with some embodimentsdescribed herein.

FIGS. 5A-5C are images of VCSEL arrays assembled in accordance with someembodiments described herein.

FIGS. 5D-5E are magnified images illustrating residual tether portionsand relief features of VCSELs in accordance with some embodimentsdescribed herein.

FIG. 6A is a perspective view illustrating an example emitter arrayincluding heterogeneous integration of distributed laser diodes anddistributed driver transistors in accordance with some embodimentsdescribed herein.

FIG. 6B is schematic view illustrating an equivalent circuit diagram forthe distributed emitter array of FIG. 6A.

FIG. 6C is a cross-sectional view of the distributed emitter array takenalong line 6C-6C′ of FIG. 6A.

FIG. 6D is schematic view illustrating an alternate equivalent circuitdiagram for the distributed emitter array of FIG. 6A.

FIG. 7A is a perspective view illustrating an example LIDAR device inaccordance with some embodiments described herein.

FIG. 7B is an exploded view illustrating example components of the LIDARdevice of FIG. 7A.

FIG. 7C is a perspective view illustrating another example LIDAR devicein accordance with some embodiments described herein.

FIG. 8 is a block diagram illustrating an example system architecturefor a LIDAR device in accordance with some embodiments described herein.

FIG. 9 is a cross-sectional view illustrating an example laser diodearray in accordance with further embodiments described herein.

FIG. 10A is a perspective view illustrating a distributed emitter arrayincluding laser diodes on a curved substrate in accordance with someembodiments described herein.

FIG. 10B is a graph illustrating an example angular power distributionoutput from a distributed emitter array including laser diodes on acurved substrate in accordance with some embodiments described herein.

FIG. 10C is a graph illustrating an example curvature of the substrateof the distributed emitter array of FIG. 10A to provide the angularpower distribution output of FIG. 10B in accordance with someembodiments described herein.

FIG. 10D is a graph illustrating an example angular power distributionoutput from a distributed emitter array including laser diodes on acurved substrate in accordance with further embodiments describedherein.

FIGS. 11A, 11B, and 11C are cross-sectional views illustrating exampledistributed emitter arrays including shaped lenslet arrays that areconfigured for high-aspect ratio beam forming in accordance with someembodiments described herein.

FIGS. 12A and 12B are cross-sectional views illustrating exampledistributed emitter arrays including a self-aligned ball lens arraysthat are configured for wide field-of-view beam forming in accordancewith some embodiments described herein.

FIGS. 13A and 13B are cross-sectional views and FIG. 13C is aperspective view illustrating example distributed emitter arraysincluding offset ball lens arrays for beam forming in accordance withsome embodiments described herein.

FIGS. 14A, 14B, and 14C are cross-sectional views illustrating exampledistributed emitter arrays including lens arrays having primary andsecondary lens elements that are configured for multi-direction beamforming in accordance with some embodiments described herein.

FIGS. 14D and 14E are graphs illustrating effects of an opticaldiffusing film on beam forming of distributed emitter arrays inaccordance with some embodiments described herein.

FIGS. 15A, 15B, 15C, 15E, and 15F are cross-sectional views and FIG. 15Dis a plan view illustrating example distributed emitter arrays includingtilted laser diodes for lensless beam forming in accordance with someembodiments described herein.

DETAILED DESCRIPTION

Embodiments described herein may arise from realization that morecompact arrays of light emitters may be advantageous in emergingtechnologies. For example, as shown in FIG. 1, a light-based 3D sensorsystem 100, such as a Light Detection and Ranging (LIDAR) system, mayuse time-of-flight (TOF)-based measurement circuit 110 and a 3D imagereconstruction circuit 150 based on a signal received from an opticaldetector circuit 130 and associated optics 140, with a pulsed lightemitting device array 120 as a light source. The time-of-flightmeasurement circuit 110 may determine the distance d to target T bymeasuring the round trip (“time-of-flight”; ToF) of a laser pulse 109reflected by the target T (where d=(speed of light (c)/2)×ToF), whichmay be used by the 3D image reconstruction circuit 150 to create anaccurate 3D map of surroundings. Some advantages of LIDAR systems mayinclude long range; high accuracy; superior object detection andrecognition; higher resolution; higher sampling density of 3D pointcloud; and effectivity in diverse lighting and/or weather conditions.Applications of LIDAR systems may include ADAS (Advanced DriverAssistance Systems), autonomous vehicles, UAVs (unmanned aerialvehicles), industrial automation, robotics, biometrics, modeling,augmented and virtual reality, 3D mapping, and security. The example ofFIG. 1 illustrates a flash LIDAR system, where the pulsed light emittingdevice array 120 emits light for short durations over a relatively largearea to acquire images, in contrast with some traditional scanning LIDARtechniques (which generate image frames by raster scanning). However, itwill be understood that light emitting device arrays 120 describedherein can be used for implementations of scanning LIDAR as well.

Still referring to FIG. 1, the light emitting device array 120 mayinclude a plurality of electrically connected surface-emitting laserdiodes, such as VCSELs, and may be operated with strong single pulses atlow duty cycle or with pulse trains, typically at wavelengths outside ofthe visible spectrum. Because of sensitivity to background light and thedecrease of the signal with distance, several watts of laser power maybe used to detect a target T at a distance d of up to about 100 metersor more.

However, some conventional VCSELs may have sizes defined by dimensions(e.g., length, width, and/or diameter) of about 150 micrometers (μm) toabout 200 μm, which may impose size and/or density constraints on sensorsystems including an array of discrete VCSELs. This relatively largeVCSEL size may be dictated for use with conventional pick-and-placemachines, as well as for sufficient contact surface area for wire bondpads to provide electrical connections to the VCSEL. For example, someconventional solder ball or wire bond technology may require more thanabout 30 μm in length for the bond pad alone, while the tip used to pullthe wire bond may have an accuracy on the order of tens of micrometers.

Some embodiments described herein provide light emitting devices, suchas surface-emitting laser diodes (e.g., VCSELs), having reduceddimensions (e.g., lengths and/or widths of about 30 micrometers (μm) orless) without affecting the device performance (e.g., power output). Forexample, the aperture of the VCSEL die (which is the active region wherethe lasing takes place) may be about 10 μm to about 20 μm in diameter.The die length can be reduced to the aperture diameter plus a fewmicrons by reducing or eliminating wasted (non-active) area, and byretaining a few microns (e.g., about 4 μm to about 6 μm or less) ofcombined chip length for the anode and the cathode contacts. This mayprovide a reduction in dimensions (e.g., length and/or width) by afactor of about 10 or more (e.g., die lengths of about 15 micrometers(μm) to about 20 μm, as compared to some conventional VCELs with dielengths of about 150 μm to about 200 μm). In some embodiments, thesereduced die dimensions may allow for fabrication of emitter arraysincluding a greater density (e.g., thousands) of VCSELs or other laserdiodes.

FIGS. 2A and 2B are plan and cross-sectional views illustrating anexample surface-emitting light emitting device (shown as a verticalcavity surface emitting laser diode (VCSEL) chip or die 200, alsoreferred to herein as a VCSEL 200) in accordance with some embodimentsdescribed herein, which includes anode and cathode contacts 211, 212that are smaller than the lasing aperture 210 in at least one dimension.As shown in FIGS. 2A and 2B, the VCSEL 200 includes an active region 205with one or more quantum wells 203 for generation and emission ofcoherent light 209. The optical cavity axis 208 of the VCSEL 200 isoriented along the direction of current flow (rather than perpendicularto the current flow as in some conventional laser diodes), defining avertical cavity with a length along the direction of current flow. Thiscavity length of the active region 205 may be short compared with thelateral dimensions of the active region 205, so that the radiation 209emerges from the surface of the cavity rather than from its edge.

The active region 205 may be sandwiched between distributed Braggreflector (DBR) mirror layers (also referred to herein as Braggreflector layers or Bragg mirrors) 201 and 202 provided on a lateralconduction layer (LCL) 206. The LCL 206 may allow for improvedelectrical and/or optical characteristics (as compared to direct contactto the reflector layer 401) in some embodiments. In some embodiments, asurface of the LCL layer 206 may provide a print interface 215 includingan adhesive layer that improves adhesion with an underlying layer orsubstrate. The adhesive layer may be optically transparent to one ormore wavelength ranges and/or can be refractive-index matched to providedesired optical performance. The reflector layers 201 and 202 at theends of the cavity may be made from alternating high and low refractiveindex layers. For example, the reflector layers 201 and 202 may includealternating layers having thicknesses d1 and d2 with refractive indicesn1 and n2 such that n1d1+n2d2=λ/2, to provide wavelength-selectivereflectance at the emission wavelength λ. This vertical construction mayincrease compatibility with semiconductor manufacturing equipment. Forexample, as VCSELs emit light 209 perpendicular to the active region205, tens of thousands of VCSELs can be processed simultaneously, e.g.,by using standard semiconductor wafer processing steps to define theemission area and electrical terminals of the individual VCSELs from asingle wafer.

Although described herein primarily with reference to VCSEL structures,it will be understood that embodiments described herein are not limitedto VCSELs, and the laser diode 200 may include other types of laserdiodes that are configured to emit light 209 along an optical axis 208that is oriented perpendicular to a substrate or other surface on whichthe device 200 is provided. It will also be understood that, whiledescribed herein primarily with reference to surface-emitting laserstructures, laser diodes and laser diode arrays as described herein arenot so limited, and may include edge-emitting laser structures that areconfigured to emit light along an optical axis that is oriented parallelto a substrate or other surface on which the device is provided as well,as shown in the example of FIG. 9.

The VCSEL 200 may be formed of materials that are selected to providelight emission at or over a desired wavelength range, which may beoutside of the spectrum of light that is visible to the human eye. Forexample, the VCSEL 200 may be a gallium arsenide (GaAs)-based structurein some embodiments. In particular embodiments, the active region 205may include one or more GaAs-based layers (for example, alternatingInGaAs/GaAs quantum well and barrier layers), and the Bragg mirrors 201and 202 may include GaAs and aluminum gallium arsenide(Al_(x)Ga_((1-x))As). For instance, the lower Bragg mirror 201 may be ann-type structure including alternating layers of n-AlAs/GaAs, while theupper Bragg mirror 202 may be a p-type structure including alternatinglayers of p-AlGaAs/GaAs. Although described by way of example withreference to a GaAs-based VCSEL, it will be understood that materialsand/or material compositions of the layers 201, 202, and/or 205 may betuned and/or otherwise selected to provide light emission at desiredwavelengths, for example, using shorter wavelength (e.g., GaN-based)and/or longer wavelength (e.g., InP-based) emitting materials.

In the example of FIGS. 2A and 2B, the VCSEL 200 includes a lasingaperture 210 having a dimension (illustrated as diameter D) of about 12μm, and first and second electrically conductive contact terminals(illustrated as anode contact 211 and cathode contact 212, also referredto herein as first and second contacts). A first electrically conductivefilm interconnect 213 is provided on the first contact 211, and a secondelectrically conductive film interconnect 213 is provided on the secondcontact 212 to provide electrical connections to the VCSEL 200. FIG. 2Bmore clearly illustrates the anode contact 211 and cathode contact 212in cross section, with the conductive film interconnects 213 thereon.The first and second contacts 211 and 212 may provide contacts tosemiconductor regions of opposite conductivity type (P-type and N-type,respectively). Accordingly, embodiments described herein are configuredfor transfer of electric energy to the VCSEL contacts 211 and 212through thin-film interconnects 213, which may be formed by patterningan electrically conductive film, rather than incorporating wire bonds,ribbons, cables, or leads. The interconnections 213 may be formed afterproviding the VCSEL 200 on a target substrate (e.g., a non-nativesubstrate that is different from a source substrate on which the VCSEL200 is formed), for example, using conventional photolithographytechniques, and may be constructed to have low resistance. In thisregard, materials for the electrically conductive film interconnects 213may include aluminum or aluminum alloys, gold, copper, or other metalsformed to a thickness of approximately 200 nm to approximately 500 nm.

As shown in FIG. 2A, the first and second conductive contacts 211 and212 are smaller than the aperture 210 in one or more dimensions. In someembodiments, allowing about 2 μm to about 3 μm for the dimensions ofeach of the contacts 211, 212, the overall dimensions of the VCSEL die200 can be significantly reduced. For example, for anode and cathodecontacts that are 2 μm in length each, a dimension L can be reduced toabout 16 μm (2 μm anode length+12 μm aperture+2 μm cathode length; allmeasured along dimension L) providing a 16×16 μm² die. As anotherexample, for anode and cathode contacts that are 3 μm in length each, adimension L can be reduced to about 18 μm (3 μm anode+12 μm aperture+3μm cathode) providing a 18×18 μm² die. Die dimensions L may be furtherreduced or slightly increased for smaller aperture dimensions D (e.g.,10 μm) or larger aperture dimensions D (e.g., 20 μm). More generally,VCSEL dies 200 according to embodiments herein may achieve a contactarea-to-aperture area ratio of about 0.05 to 30, about 0.1 to 20, about1 to 10, or about 1 to 3, where the contact area refers to the surfacearea of electrical contacts 211 and/or 212 positioned on or adjacent theaperture 210 on the surface S. Also, although illustrated with referenceto contacts 211, 212 and interconnections 213 at particular locationsrelative to the aperture 210, it will be understood that embodimentsdescribed herein are not so limited, and the contacts 211, 212 andinterconnections 213 may be provided at other areas of the VCSEL die 200(e.g., at corners, etc.).

VCSELs 200 in accordance with some embodiments described herein may beconfigured to emit light with greater than about 100 milliwatts (mW) ofpower within about a 1-10 nanosecond (ns) wide pulse width, which may beuseful for LIDAR applications, among others. In some embodiments, morethan 1 Watt peak power output with a 1 ns pulse width at a 10,000:1 dutycycle may be achieved from a single VCSEL element 200, due for instanceto the reduced capacitance (and associated reduction in RLC timeconstants) as compared to some conventional VCSELs. VCSELs 200 asdescribed herein may thus allow for longer laser lifetime (based uponlow laser operating temperatures at high pulsed power), in combinationwith greater than about 200 meter (m) range (based on very high poweremitter and increased detector sensitivity).

FIG. 2C is a plan view illustrating the VCSEL chip 200 in accordancewith some embodiments described herein in comparison to a conventionalVCSEL chip 10. As shown in FIG. 2C, the conventional VCSEL chip 10 mayhave a length L of about 200 μm, to provide sufficient area for theactive region 5 and the top conductive wire bond pad 11, which mayfunction as an n-type or p-type contact. In contrast, VCSEL chips 200 inaccordance with some embodiments described herein may have a length L ofabout 20 μm or less. As electrical connections to the smaller contacts211, 212 are provided by thin-film metallization interconnects 213,VCSEL chips 200 in accordance with some embodiments described hereinrequire no bond pad, such that the optical aperture 210 occupies amajority of the overall surface area of the emitting surface S.

VCSEL chips 200 according to some embodiments of the present inventionmay thus have dimensions that are 1/100^(th) of those of someconventional VCSEL chips 10, allowing for up to one hundred times morepower per area of the emitting surface S, as well as reduced capacitancewhich may substantially reduce the RLC time constants associated withdriving fast pulses into these devices. Such an exponential reduction insize may allow for fabrication of VCSEL arrays including thousands ofclosely-spaced VCSELs 200, some of which are electrically connected inseries (or anode-to-cathode) on a rigid or flexible substrate, which maynot be possible for some conventional closely spaced VCSELs that arefabricated on a shared electrical substrate. For example, as describedin greater detail below, multiple dies 200 in accordance with someembodiments described herein may be assembled and electrically connectedwithin the footprint of the conventional VCSEL chip 10. In someapplications, this size reduction and elimination of the bond pad mayallow for reduction in cost (of up to one hundred times), devicecapacitance, and/or device thermal output, as compared to someconventional VCSEL arrays.

FIG. 3A is a perspective view illustrating a distributed emitter array300 a including laser diodes (illustrated as VCSELs 200) in accordancewith some embodiments described herein. The array 300 a (also referredto herein as a distributed VCSEL array (DVA)) may be assembled on anon-native substrate 307 a, for example, by micro-transfer printing,electrostatic adhesion, or other mass transfer techniques. As usedherein, a non-native substrate (also referred to herein as a targetsubstrate) may refer to a substrate on which the laser diodes 200 arearranged or placed, which differs from a native substrate on which thelaser diodes 200 are grown or otherwise formed (also referred to hereinas a source substrate). The substrate 307 a may be rigid in someembodiments, or may be flexible in other embodiments, and/or may beselected to provide improved thermal characteristics as compared to thesource substrate. For example, in some embodiments the non-nativesubstrate 307 a may be thermally conducting and also electricallyinsulating (or coated with an insulating material, such as an oxide,nitride, polymer, etc.). Electrically conductive thin-film interconnects313 may be formed to electrically connect respective contacts of thelaser diodes 200 in series and/or parallel configurations, and may besimilar to the interconnects 213 described above. This may allow fordynamically adjustable configurations, by controlling operation ofsubsets of the laser diodes 200 electrically connected by the conductivethin-film interconnects 313. In some embodiments, the array 300 a mayinclude wiring 313 between VCSELs 200 that are not connected in parallel(e.g., connections without a shared or common cathode/anode). That is,the electrically conductive thin-film interconnects 313 may providenumerous variations of series/parallel interconnections, as well asadditional circuit elements which may confer good yield (e.g. bypassroutes, fuses, etc.).

The conductive thin-film interconnects 313 may be formed in a parallelprocess, before and/or after providing the laser diodes 200 on thesubstrate 307 a. For example, the conductive thin-film interconnects 313may be formed by patterning an electrically conductive film on thesubstrate 307 a using conventional photolithography techniques, suchthat the laser diodes 200 of the array 300 are free of electricalconnections through the substrate 307 a.

Due to the small dimensions of the laser diodes 200 and the connectionsprovided by the conductive thin-film interconnects 313, a spacing orpitch between two immediately adjacent laser diodes 200 is less thanabout 500 micrometers (μm), or in some embodiments, less than about 200μm, or less than about 150 μm, or less than about 100 μm, or less thanabout 50 μm, without connections to a shared or common cathode/anode.While some monolithic arrays may provide inter-laser diode spacings ofless than about 100 μm, the laser diodes of such arrays may electricallyshare a cathode/anode and may mechanically share a rigid substrate inorder to achieve such close spacings. In contrast, laser diode arrays asdescribed herein (such as the array 300 a) can achieve spacings of lessthan about 150 μm between immediately adjacent, serially-connected laserdiodes 200 (that do not have a common anode or cathode connection), onnon-native substrates (e.g., rigid or flexible substrates) in someembodiments. In addition, as described below with reference to theexamples of FIGS. 6A-6C, some embodiments of the present disclosure mayintegrate other types of devices and/or devices formed from differentmaterials (e.g. power capacitors, FETs, etc.) in-between laser diodes200 at the sub-150 μm spacings described herein.

Also, in some embodiments, a concentration of the laser diodes 200 perarea of the array 300 a may differ at different portions of the array300 a. For example, some LIDAR sensor applications may benefit fromhigher resolution in a central portion of the array (corresponding to aforward direction of travel), but may not require such high resolutionat peripheral regions of the array. As such, a concentration of VCSELs200 at peripheral portions of the array 300 a may be less than aconcentration of VCSELs 200 at a central portion of the array 300 a insome embodiments. This configuration may be of use in applications wherethe substrate is flexible and may be curved or bent in a desired shape,as shown in FIG. 3B.

FIG. 3B is a perspective view illustrating a distributed emitter array300 b including laser diodes 200 on a curved, non-native substrate 307 bin accordance with some embodiments described herein. In someembodiments, the substrate 307 b is formed of a flexible material thatcan be bent to provide curved emitting surface, such that VCSELs 200mounted on a central portion 317 of the substrate 307 b face a forwarddirection, while VCSELs 200 mounted on peripheral portions 317′ of thesubstrate 307 b face oblique directions. As the VCSELs 200 respectivelyemit light in a direction perpendicular to their active regions, theVCSELs 200 mounted on the central portion 317 emit light 309 in theforward direction, while the VCSELs 200 mounted on peripheral portions317′ of the substrate 307 b emit light 309′ in oblique directions,providing a wide field of view. In some embodiment, each VCSEL mayprovide narrow-field illumination (e.g., covering less than about 1degree), and the arrays 300 a, 300 b may include hundreds or thousandsof VCSELs 200 (e.g., an array of 1500 VCSELs, each covering a field ofview of about 0.1 degree, can provide a 150 degree field of view).

The field of view can be tailored or changed as desired from 0 degreesup to about 180 degrees by altering the curvature of the substrate 307b. The curvature of the substrate 307 b may or may not be constantradius, and can thereby be designed or otherwise selected to provide adesired power distribution. For example, the substrate 307 b may definea cylindrical, acylindrical, spherical or aspherical curve whose normalsurfaces provide a desired distribution of relative amounts of power. Insome embodiments, the curvature of the substrate 307 b may bedynamically altered by mechanical or electro-mechanical actuation. Forexample, a mandrel can be used to form the cylindrical or acylindricalshape of the flexible non-native substrate 307 b. The mandrel can alsoserve as a heat sink in some embodiments. Also, as mentioned above, aspatial density or concentration of VCSELs 200 at peripheral portions ofthe array 300 b may be less than a concentration of VCSELs 200 at acentral portion of the array 300 b in some embodiments. For example,rows or columns of the array 300 b of VCSELs 200 may be arranged on thenon-native substrate 307 b at different and/or non-uniform pitches toprovide a desired far-field output light pattern, for instance, usingmicro-transfer printing and/or other micro-assembly techniques.

The arrays 300 a and 300 b illustrated in FIGS. 3A and 3B may bescalable based on a desired quantity or resolution of laser diodes 200,allowing for long range and high pulsed power output (on the order ofkilowatts (kW)). The spatial density or distribution of the laser diodes200 on the surfaces of the substrates 307 a and 307 b can be selected toreduce optical power density, providing both long range and eye safetyat a desired wavelength of operation (e.g., about 905 nm for GaAsVCSELs; about 1500 nm for InP VCSELs). A desired optical power densitymay be further achieved by controlling the duty cycle of the signalsapplied to the VCSELs and/or by altering the curvature of the substrate.Also, the separation or spacing between adjacent laser diodes 200 withinthe arrays 300 a and 300 b may be selected to provide thermal managementand improve heat dissipation during operation, depending on thesubstrate material. For example, a spacing between two immediatelyadjacent laser diodes 200 of greater than about 100 μm micrometers (μm)may provide thermal benefits, especially for substrates with limitedthermal conductivity. The arrays 300 a and 300 b as described herein maythereby provide greater reliability, by eliminating wire bonds,providing a fault-tolerant architecture, and/or providing loweroperating temperatures. In further embodiments, self-aligning, low-costbeam forming micro-optics (e.g., ball lens arrays) may be integrated onor into the surface of the arrays 300 a and 300 b.

The compact arrays 300 a and 300 b shown in FIGS. 3A and 3B may befabricated in some embodiments using micro-transfer printing (MTP),electrostatic adhesion, and/or other massively parallel chip handlingtechniques that allow simultaneous assembly and heterogeneousintegration of thousands of micro-scale devices on non-native substratesvia epitaxial liftoff For example, the arrays of VCSELs 200 can befabricated using micro-transfer printing processes similar to thosedescribed, for example, in U.S. Pat. No. 7,972,875 to Rogers et al.entitled “Optical Systems Fabricated By Printing-Based Assembly,” thedisclosure of which is incorporated by reference herein in its entirety.The arrays of VCSELs 200 can alternatively be fabricated usingelectrostatic adhesion or gripping transfer techniques similar to thosedescribed, for example in U.S. Pat. No. 8,789,573 to Bibl et al.entitled “Micro device transfer head heater assembly and method oftransferring a micro device,” the disclosure of which is incorporated byreference herein in its entirety. In some embodiments, MTP,electrostatic adhesion, and/or other mass transfer techniques may allowfor fabrication of VCSEL or other arrays of laser diodes with the smallinter-device spacings described herein.

FIGS. 4A-4F are perspective views and FIGS. 4A′-4G′ are cross-sectionalviews illustrating an example fabrication process for laser diodes(illustrated as VCSELs 400) in accordance with some embodimentsdescribed herein. The VCSELs 200 described herein may also be fabricatedusing one or more of the processing operations shown in FIGS. 4A-4F insome embodiments. As shown in FIGS. 4A-4F and FIGS. 4A′-4G′, ultra smallVCSELs 400 in accordance with embodiments described herein can be grownon source substrates and assembled on a non-native target substrateusing micro-transfer printing techniques. In particular, in FIGS. 4A and4A′, sacrificial layer 408, a lateral conduction layer 406, a first,n-type distributed Bragg reflector (DBR) layer 401, an active region405, and a second, p-type DBR layer 402 are sequentially formed on asource wafer or substrate 404. Although illustrated with reference to asingle VCSEL 400 to show fabrication, it will be understood that aplurality of VCSELs 400 may be simultaneously fabricated on the sourcewafer 404, with reduced or minimal spacing between adjacent VCSELs 400to increase or maximize the number of VCSELs that may be simultaneouslyfabricated on the wafer 404. Also, it will be understood that aplurality of VCSEL devices may be fabricated on a single die or chipletthat is released from the substrate 404 for printing. Also, the transfertechniques described in greater detail below may allow for reuse of thesource wafer 404 for subsequent fabrication of additional VCSELs.

In some embodiments, the material compositions of the layers 406, 401,405, and 402 may be selected to provide a desired emission wavelengthand emission direction (optical axis). For example, the layers 406, 401,405, and 402 may be gallium arsenide (GaAs)-based or indium phosphide(InP)-based in some embodiments. As illustrated, a lateral conductionlayer 406, an AlGaAs n-type high-reflectivity distributed Braggreflector (DBR), and an active region 405 are sequentially formed on thesource wafer 404. The active region 405 may be formed to includeInAlGaAs strained quantum wells designed to provide light emission overa desired wavelength, and is followed by formation of a p-type DBRoutput mirror 402. A top contact metallization process is performed toform a p-contact (e.g., an anode contact) 411 on the p-type DBR layer402. For example, Ti/Pt/Au ring contacts of different dimensions may bedeposited to form the anode or p-contact 411. An aperture 410 may bedefined within a perimeter of the p-contact 411. In some embodiments, anoxide layer may be provided between the active region 405 and the p-typeDBR layer 402 to define boundaries of the aperture 410. The placementand design of the aperture 410 may be selected to minimize opticallosses and current spreading.

In FIGS. 4B and 4B′, a top mesa etching process is performed to exposethe active region 405 and a top surface of the n-type DBR layer 401, andan oxidation process is performed to oxidize the exposed surfaces,(including the exposed sidewalls of the active region 405), and inparticular to laterally define boundaries of the optical aperture 410.In FIGS. 4C and 4C′, a bottom contact metallization process is performedto expose and form an n-type (e.g., cathode) contact 412 on a surface ofthe lateral conduction layer 406. It will be understood that, in someembodiments, the n-type contact 412 may alternatively be formed on then-type DBR layer 401 to provide the top-side contact. In FIGS. 4D and4D′, an isolation process is performed to define respective lateralconduction layers 406, and an anchor material (e.g., photoresist layer)is deposited and etched to define photoresist anchors 499 and inlets toexpose sacrificial release layer 408 for epitaxial lift-off.

In FIGS. 4E and 4E′, an undercut etching process is performed to removeportions of the sacrificial release layer 408 such that the anchors 499suspend the VCSEL die 400 over the source wafer 404. In someembodiments, the operations of FIGS. 4E and 4E′ may be followed by amicro-transfer printing process, as shown in FIGS. 4F and 4F′, which mayutilize an elastomeric and/or other stamp 490 to break the anchors 499,adhere the VCSEL die 400 (along with multiple other VCSEL dies 400 onthe source wafer 404) to a surface of the stamp 490, and simultaneouslytransfer the multiple VCSEL dies 400 (which have been adhered to thesurface of the stamp) to a non-native target substrate 407 by contactingthe surface of the stamp including the dies 400 thereon with a surfaceof the non-native target substrate 407, as shown in FIG. 4G′. In otherembodiments, the operations of FIG. 4F may be followed by anelectrostatic gripper-based transfer process, which may utilize anelectrostatic transfer head to adhere the VCSEL die 400 (along withmultiple other VCSEL dies 400 on the source wafer 404) to a surface ofthe head using the attraction of opposite charges, and simultaneouslytransfer the VCSEL dies 400 to a non-native target substrate. As aresult of breaking the anchors 499, each VCSEL die 400 may include abroken or fractured tether portion 499 t (e.g., a residual portion ofthe anchor structure 499) protruding from or recessed within an edge orside surface of the die 400 (and/or a corresponding relief feature at aperiphery of the die 400), which may remain upon transfer of the VCSELdies 400 to the non-native substrate 407.

The non-native target substrate may be a rigid or flexible destinationsubstrate for the VCSEL array, or may be a smaller interposer or“chiplet” substrate. Where the target substrate is the destinationsubstrate for the array, an interconnection process may form aconductive thin film layer on the target substrate including theassembled VCSEL dies 400 thereon, and may pattern the conductive thinfilm layer to define thin-film metal interconnects that provide desiredelectrical connections between the VCSEL dies 400. The interconnectionprocess may be performed after the VCSEL dies 400 are assembled on thedestination substrate, or may be performed in a pre-patterning processon the destination substrate before the VCSEL dies 400 are assembledsuch that the electrical connections between the VCSEL dies 400 arerealized upon assembly (with no interconnection processing requiredafter the transfer of the dies 400 onto the substrate). Where the targetsubstrate is a chiplet, the VCSEL dies 400 may be connected in parallelvia the chiplet. The chiplets including the VCSEL dies 400 thereon maythen be assembled (via transfer printing, electrostatic adhesion, orother transfer process) onto a destination substrate for the array,which may be pre- or post-patterned to provide electrical connectionsbetween the chiplets. The thin-film metal interconnects may be definedon and/or around the broken tether portion protruding from the edge ofthe die(s) 400 in some embodiments.

Because the VCSELs 400 are completed via epitaxial lift-off and thus areseparated from the substrate, and because of the use of thin filminterconnects, the VCSELs 400 may also be thinner than some conventionalVCSELs which remain connected to their native substrate, such as theVCSEL 10 of FIG. 2C. For example, the VCSEL 400 may have a thickness t(e.g., a combined thickness of the semiconductor stack including thelayers 406, 401, 405, and 402) of about 1 micrometers (μm) to about 20μm.

FIGS. 5A-5C are images of VCSEL arrays 500 in accordance with someembodiments described herein, which were assembled using micro-transferprinting processes. In particular, FIG. 5A illustrates a VCSEL array 500of about 11,000 lasers with an inter-VCSEL spacing of about 200micrometers (μm) or less between adjacent VCSELs 200 after assembly on anon-native substrate 507, with the inset image of FIG. 5B and the imageof 5C illustrating a magnified views of portions of the array 500including about 350 lasers and 9 lasers, respectively, in accordancewith some embodiments described herein. Due to the reduction indimensions of the VCSELs described herein, the inter-VCSEL spacingbetween immediately adjacent VCSELs 200 may be less than about 150 μm,or less than about 100 μm or less than about 50 μm on the sourcesubstrate in some embodiments. In some embodiments, the array 500 mayinclude 100 VCSELs or more within a footprint or area of 5 squaremillimeters (mm²) or less.

FIGS. 5D-5E are magnified images illustrating broken tether portions andrelief features of VCSEL structures in accordance with some embodimentsdescribed herein. As shown in FIGS. 5D and 5E, a transfer-printed VCSEL510 (such as one of the VCSELs 200) or other laser diode as describedherein may include one or more broken tether portions 499 t and/orrelief features 599 at a periphery thereof. The relief features 599 maybe patterned or otherwise provided along the periphery of VCSEL 510 topartially define the tethers 499 and areas for preferential fracture ofthe tethers 499. In the examples of FIGS. 5D-5E, the broken tetherportions 499 t and relief features 599 are illustrated as being presentalong a periphery of the lateral conduction layer (LCL) 506; however, itwill be understood that broken tether portions 499 t and/or relieffeatures 599 may be present in or along a periphery of any of the layersthat may be provided on a non-native substrate by transfer-printingprocesses described herein, for example, any of the epitaxially grownlayers 406, 405, 401, 402 formed in fabricating the active region 405 ona source wafer or substrate 404 in the examples of FIGS. 4A-4F and4A′-4G′. As such, in some embodiments, the broken tether portion 499 tmay comprise a material and thickness corresponding to that of the LCLlayer 506 (or other layer associated with the active region). In furtherembodiments, to shorten an etch sequence, peripheral or edge portions ofthe LCL 506 may be partially etched, and as such, the relief pattern 599of the tether features 499 t may be thinner than the LCL 506 (or otherlayer associated with the active region). The fracture of the tethers499 during the “Pick” operation (such as shown in FIG. 4G′) may occur inthe resist layer 499 l itself, and the broken tether portions 499 t maycomprise a material and thickness corresponding to that of the resistlayer 499 l. The broken tether portion 499 t may interact with the printadhesive or epoxy, and also remains on the fully processed device, evenafter resist develop and/or resist removal processes. More generally,some laser diode structures in accordance with embodiments describedherein may include at least one of a broken tether portion 499 t or arelief pattern or feature 599 at areas adjacent the tethers 499 along aperiphery or edge of the laser diode structure.

Accordingly, some embodiments described herein may use MTP to print andintegrate hundreds or thousands of VCSELs or other surface-emittinglaser diodes into small-footprint light-emitting arrays. MTP may beadvantageous by allowing simultaneous manipulation and wafer-levelassembly of thousands of laser diode devices. In some embodiments, eachof the laser diodes may have aperture dimensions as small as about 1-10μm, thereby reducing the size (and cost) of lasers incorporating suchVCSEL arrays by a factor of up to 100. Other embodiments may includesubstrates with aperture dimensions even smaller than about 1 μm inorder to realize different performance such as modified near and farfield patterns. Still other embodiments may use larger apertures, forexample, about 10-100 μm, in order to realize higher power output perVCSEL device. Also, MTP allows reuse of the source wafer (e.g., GaAs orInP) for growth of new devices after the transfer printing process,further reducing fabrication costs (in some instances, by up to 50%).MTP may also allow heterogeneous integration and interconnection oflaser diodes of different material systems (e.g., GaAs or InP lasers)and/or driver transistors (as discussed below) directly onto siliconintegrated circuits (ICs). Also, source wafers may be used and reused ina cost-effective manner, to fabricate laser diodes (e.g., InP-basedVCSELs) that can provide high power with eye safety, as well as reducedambient noise. As such, MTP may be used in some embodiments to reduceemitter costs, and allow fabrication of high power, high resolutiondistributed VCSEL arrays (DVAs) including multiple hundreds or thousandsof VCSELs.

Also, when provided on flexible or curved substrates, embodimentsdescribed herein can provide DVAs having a wide field of view (FoV), upto 180 degrees horizontal. In some embodiments, the optical powerdispersed via the DVA can be configured for eye safety and efficientheat dissipation. In some embodiments, low-cost, self-aligning, beamforming micro-optics may be integrated within the curved DVA.

FIG. 6A is a perspective view illustrating an example emitter array 600including heterogeneous integration of distributed surface-emittinglaser diodes (illustrated as VCSELs 200) and distributed drivertransistors 610 in accordance with some embodiments described herein. Asused herein, distributed circuit elements may refer to laser diodes,driver transistors, and/or other circuit elements that are assembled invarious desired positions throughout a laser diode array, and such anarray of distributed circuit elements is referred to herein as adistributed array. For example, integration of distributed high powerdriver transistors in a distributed VCSEL array may be advantageous forLIDAR applications. FIG. 6B is schematic view illustrating an equivalentcircuit diagram for the distributed emitter array 600 of FIG. 6A, andFIG. 6C is a cross-sectional view of the distributed emitter array 600taken along line 6C-6C′ of FIG. 6A.

As shown in FIGS. 6A-6C, the array 600 (also referred to herein as aDVA) may be assembled on a non-native substrate 607, for example, bymicro-transfer printing or other techniques. The substrate 607 may berigid in some embodiments, or may be flexible in other embodiments. Thearray 600 further includes integrated driver transistors 610 that areassembled on the substrate 607 adjacent to one or more of the VCSELs200. In some embodiments, the drivers 610 and laser diodes 200 mayinclude different semiconductor materials and/or technologies that haveincompatible fabrication processes. For example, the driver transistors610 may be assembled on the substrate 607 using a micro-transferprinting (MTP) process. In some embodiments, an array including hundredsor thousands of driver transistors 610 may be provided. Electricallyconductive thin-film interconnects 613 may be formed to electricallyconnect respective contacts of the driver transistors 610 and laserdiodes 200 in series and/or parallel configurations. Spacings between adriver transistor 610 and an immediately adjacent laser diodes 200 maybe less than about 2 millimeters, less than about 1 millimeter, lessthan about 500 micrometers, less than about 150 micrometers (μm), or insome embodiments, less than about 100 μm, or less than about 50 μm,which may provide reduced parasitic impedance therebetween (e.g., up to100 times lower than where the driver transistor 610 is located off-chipor off-substrate).

In some embodiments, the array 600 may include wiring 613 between VCSELs200 that are not connected in parallel (e.g., no common cathode/anode).Interconnection designs that do not simply place all elements of thearray in parallel (e.g., without a common anode or cathode connection)may offer the advantage of lowering current requirements for the array,which can reduce inductive losses and increase switching speed. Variedinterconnection designs also provide for the inclusion of other devicesembedded or integrated within the electrically interconnected array(e.g., switches, gates, FETs, capacitors, etc.) as well as structureswhich enable fault tolerance in the manufacture of the array (e.g.fuses, bypass circuits, etc.) and thus confer yield advantages. Forexample, as illustrated in FIG. 6B, the array 600 includes a pluralityof strings of VCSELs 200 that are electrically connected in series (oranode-to-cathode) to define columns (or other subsets or sub-arrays) ofthe array 600. The array 600 further includes an array of drivertransistors 610, with each driver 610 electrically connected in serieswith a respective string of serially-connected (or otherwiseanode-to-cathode-connected) VCSELs 200.

The conductive thin-film interconnects 613 may be formed in a parallelprocess after providing the laser diodes 200 and driver transistors 610on the substrate 607, for example by patterning an electricallyconductive film using conventional photolithography techniques. As such,the driver transistors 610 and laser diodes 200 of the array 600 arefree of wire bonds and/or electrical connections through the substrate607. Due to the smaller dimensions of the laser diodes 200 and thedriver transistors 610 and the degree of accuracy of the assemblytechniques described herein, a spacing between immediately adjacentlaser diodes 200 and/or driver transistors 610 may be less than about150 micrometers (μm), or in some embodiments, less than about 100 μm orless than about 50 μm. Integrating the driver transistors 610 on thesubstrate 607 in close proximity to the VCSELs 200 (for example, atdistances less than about 2 millimeters, less than about 1 millimeter,less than about 500 micrometers, less than about 150 micrometers (μm),or in some embodiments, less than about 100 μm, or less than about 50 μmfrom a nearest VCSEL 200) may thus shorten the electrical connections613 between elements, thereby reducing parasitic resistance, inductance,and capacitance, and allowing for faster switching response.

In the example of FIGS. 6A-6C, the driver transistors 610 are arrangedin an array such that each driver transistor 610 is connected in serieswith a column (or other subset) of serially-connected (or otherwiseanode-to-cathode-connected) VCSELs 200, allowing for individual controlof respective columns/strings of VCSELs 200. However, it will beunderstood that embodiments described herein are not limited to such aconnection configuration. To the contrary, integrating the drivertransistors 610 in close proximity to the VCSELs 200 may also allow forgreater flexibility in wiring configurations (e.g., in series and/orparallel), which may be used to control current and/or increase ormaximize performance. For example, fewer or more driver transistors 610may be provided (e.g., drivers for control of rows of serially-connectedVCSELs 200 as well as columns) for finer control of respective VCSELs orgroups of VCSELs and/or output power. Another example would be theaddition of capacitors or similar electrical storage devices close tothe elements of the array for faster pulse generation, for example, onthe order of sub-nanosecond (ns), in contrast to some conventionaldesigns that may be on the order of about 1-10 ns or more. Likewise,although illustrated as a planar array 600, the substrate 607 may beflexible in some embodiments; thus, the array 600 may be bent to providea desired curvature, similar to the array 300 b of FIG. 3B.

As similarly discussed above with reference to the arrays 300 a and 300b, the array 600 may be scalable based on a desired quantity orresolution of laser diodes 200, allowing for long range and high pulsedpower output (on the order of kilowatts (kW)). The distribution of thelaser diodes 200 on the surfaces of the substrate 607 can be selectedand/or the operation of the laser diodes can be dynamically adjusted orotherwise controlled (via the transistors 610) to reduce optical powerdensity, providing both long range and eye safety at a desiredwavelength of operation (e.g., about 905 nm for GaAs VCSELs; about 1500nm for InP VCSELs). Also, the spacing between elements 200 and/or 610may be selected to provide thermal management and improve heatdissipation during operation. Arrays 600 as described herein may therebyprovide improved reliability, by eliminating wire bonds, providing afault-tolerant architecture, and/or providing lower operatingtemperatures. In further embodiments, self-aligning, low-cost beamforming micro-optics (e.g., ball lens arrays) may be integrated on orinto the surface of the substrate 607, as discussed below with referenceto FIGS. 12A-12B.

FIG. 6D is a schematic view illustrating an equivalent circuit diagramof the distributed emitter array 600 of FIG. 6A in which the emitters200 are individually addressable. As illustrated in FIG. 6D, the array600 includes a plurality of strings of VCSELs 200 that are electricallyconnected in series (or anode-to-cathode) to define columns or othersubsets or sub-arrays of the array 600. The array 600 further includesan array of driver transistors 610, with each driver transistor 610electrically connected in series with a respective string ofserially-connected VCSELs 200. The driver transistors 610 may beindividually addressable via column signals COLUMN. In some embodiments,the driver transistors 610 may be individually activated (e.g., biasedso as to be conducting) so as to vary power provided to a respectivestring of the serially-connected VCSELs 200. In some embodiments, thedriver transistors 610 may be operated in linear mode so as to vary aresistance of the driver transistor 610 and accordingly vary a currentapplied to the string of serially-connected (or otherwiseanode-to-cathode-connected) VCSELs 200.

Rows of the array 600 may also be individually addressable. For example,the array 600 may utilize bypass circuits to individually select one ofthe rows of the string of serially connected VCSELs 200. In someembodiments, individual bypass transistors 628 may be utilized to selectrespective ones of the VCSELs 200. For example, to select a particularVCSEL 200 at a particular row and column, the driver transistor 610 forthe string containing the particular VCSEL 200 may be activated toprovide current through the string, and the bypass transistor 628associated with the particular VCSEL 200 may be turned off (e.g., biasedso as to be non-conducting) so that current through the string may flowthrough the VCSEL 200. In some embodiments, the bypass transistor 628may be operated in linear mode to provide a variable resistance alongthe bypass path. The variable resistance may allow for control of theamount of current flowing through the VCSEL 200.

The circuit embodiment of FIG. 6D is merely an example of how the arrayof emitters 600 may be configured to be both row and column addressable.However, the embodiments described herein are not limited to thisparticular arrangement. One of ordinary skill in the art will recognizethat other potential circuit arrangements are possible to implement anactive matrix of devices that may be selectively addressed by both rowand column, for example, to direct a larger fraction of pulse energy tosome subset of the VCSELs in order to modify the far field pattern ofthe emitted output beam, such that only certain directions are receivinga greater amount of power. Such circuit arrangements may be used insteadof the circuit arrangement of FIG. 6D without deviating from the scopeof the embodiments described herein.

FIG. 7A is a perspective view illustrating a LIDAR device 700 aincluding surface-emitting laser diodes (such as the VCSELs 200) inaccordance with embodiments described herein, illustrated relative to apencil for scale. FIG. 7C is a perspective view illustrating analternative LIDAR device 700 c in accordance with embodiments describedherein. In particular, FIGS. 7A and 7C illustrate a distributedvertical-cavity-surface-emitting laser (VCSEL) array-based, solid-stateFlash LIDAR device 700 a, 700 c. The LIDAR device 700 a, 700 c isillustrated with reference to a curved array 720, such as the curvedarray 300 b of FIG. 3B, but it will be understood that the LIDAR device700 a, 700 c is not so limited, and may alternatively implement thearray 300 a of FIG. 3A, the array 600 of FIGS. 6A-6C, and/or otherarrays of laser diodes 200 that provide features described herein. Suchfeatures of the device 700 a, 700 c may include, but are not limited to,broad field of view (in particular embodiments, about θ=120° horizontalby ϕ=10° vertical, or broader); long range (in some instances, greaterthan about 200 m); high resolution (in particular embodiments, about0.1° horizontal and vertical) compact size defined by reduced dimensions(in particular embodiments, about 110×40×40 mm); high power (inparticular embodiments, about 10,000 w peak, pulsed); and eye safety (inparticular embodiments, dispersed optical power can support eye safe,high power, 905 nm (e.g., GaAs) and/or about 1500 nm (e.g., InP)emitters).

FIG. 7B is an exploded view 700 b illustrating components of the LIDARdevice 700 a of FIG. 7A. As shown in FIG. 7B, the device housing orenclosure 701 includes a connector 702 for electrical connection to apower source and/or other external devices. The enclosure 701 is sizedto house a light emitter array 720, a light detector array 730,electronic circuitry 760, detector optics 740 (which may include one ormore lenses and/or optical filters), and a lens holder 770. Atransparent cover 780 is provided to protect the emitter array 720 anddetector optics 740, and may include beam shaping and/or filteringoptics in some embodiments.

The light emitter array 720 may be a pulsed laser array, such as any ofthe VCSEL arrays 300 a, 300 b, 600 described herein. As such, the lightemitter array 720 may include a large quantity (e.g., hundreds or eventhousands) of distributed, ultra small laser diodes 200, which arecollectively configured to provide very high levels of power (byexploiting benefits of the large number of very small devices). Using alarge number of small devices rather than a small number of largedevices allows devices that are very fast, low power and that operate ata low temperature to be integrated in an optimal configuration (withother devices, such as transistors, capacitors, etc.) to provideperformance not as easily obtained by a small number of larger laserdevices. As described herein the laser diodes 200 may be transferprinted simultaneously onto a non-native curved or flexible substrate insome embodiments. Beam shaping optics that are configured to projecthigh aspect ratio illumination from the light emitter array 720 onto atarget plane may also be provided on or adjacent the light emitter array720.

The light detector array 730 may include one or more optical detectordevices, such as pin, pinFET, linear avalanche photodiode (APD), siliconphotomultiplier (SPM), and/or single photon avalanche diode (SPAD)devices, which are formed from materials or otherwise configured todetect the light emitted by the light emitter array 720. The lightdetector array 730 may include a quantity of optical detector devicesthat are sufficient to achieve a desired sensitivity, fill factor, andresolution. In some embodiments, the light detector array 730 may befabricated using micro-transfer printing processes as described herein.The detector optics 740 may be configured to collect high aspect ratioecho and focus target images onto focal plane of the light detectorarray 730, and may be held on or adjacent the light detector array 730by the lens holder 770.

The electronic circuitry 760 integrates the above and other componentsto provide multiple return LIDAR point cloud data to data analysis. Moreparticularly, the electronic circuitry 760 is configured to controloperation of the light emitter array 720 and the light detector array730 to output filtered, high-quality data, such as 3D point cloud data,to one or more external devices via the connector 702. The externaldevices may be configured to exploit proprietary and/or open source 3Dpoint cloud ecosystem and object classification libraries for analysisof the data provided by the LIDAR device 700 a, 700 c. For example, suchexternal devices may include devices configured for applicationsincluding but not limited to autonomous vehicles, ADAS, UAVs, industrialautomation, robotics, biometrics, modeling, augmented and virtualreality, 3D mapping, and/or security.

FIG. 8 is a block diagram illustrating an example system 800 for a LIDARdevice, such as the LIDAR device 700 a, 700 b, 700 c of FIGS. 7A-7C, inaccordance with some embodiments described herein. As shown in FIG. 8,the system 800 integrates multiple electrically coupled integratedcircuit elements to provide the LIDAR device functionality describedherein. In particular, the system 800 includes a processor 805 that iscoupled to a memory device 810, an illumination circuit 820, and adetection circuit 830. The memory device 810 stores computer readableprogram code therein, which, when executed by the processor, operatesthe illumination circuit 820 and the detection circuit 830 to collect,process, and output data, such as 3D point cloud data, indicative of oneor more targets in the operating environment. The system 800 may furtherinclude a thermistor 842 and associated temperature compensation circuit843, as well as a power management circuit 841 that is configured toregulate voltage or power to the system 800.

The illumination circuit 820 includes an array of discretesurface-emitting laser diodes 200, driver transistor(s) 610, andassociated circuit elements 611, electrically connected in any ofvarious configurations. In some embodiments, the illumination circuit820 may be a laser array including rows and/or columns of VCSELs 200,such as any of the VCSEL arrays 300 a, 300 b, 600 described herein.Operation of the illumination circuit 820 to emit light pulses 809 maybe controlled by the processor 805 via a modulation and timing circuit815 to generate a pulsed light output 809. Beam-shaping and/or focusingoptics, such as the lens arrays shown in FIGS. 11A-14C, may also beincluded in or adjacent the array of laser diodes 200 to shape and/ordirect the light pulses 809.

The detection circuit 830 may include a time-of-flight (ToF) detector851 coupled to a ToF controller 852. The ToF detector 851 may includeone or more optical detector devices, such as an array of discrete pin,pinFET, linear avalanche photodiode (APD), silicon photomultiplier(SPM), and/or single photon avalanche diode (SPAD) devices. The ToFcontroller 852 may determine the distance to a target by measuring theround trip (“time-of-flight”) of a laser pulse 809′ reflected by thetarget and received at the ToF detector 851. In some embodiments, thereflected laser pulse 809′ may be filtered by an optical filter 840,such as a bandpass filter, prior to detection by the ToF detector 851.The output of the detection block 830 may be processed to suppressambient light, and then provided to the processor 805, which may performfurther processing and/or filtering (via signal processor discriminatorfilter 817, and may provide the filtered output data (for example, 3Dpoint cloud data) for data analysis. The data analysis may include framefiltering and/or image processing. In some embodiments, the dataanalysis may be performed by an external device, for example, anautonomous vehicle intelligence system.

FIG. 9 is a cross-sectional view illustrating an example laser diodearray 900 including edge-emitting laser diodes 910 in accordance withfurther embodiments described herein. As shown in FIG. 9, a laser diode910 includes an active region 905 (which may include one or more quantumwells) for generation and emission of coherent light 909. The activeregion 905 is provided between p-type and n-type layers 901 and 902,with contacts 912 and 911 thereon, respectively. A diffraction gratinglayer may be included to provide feedback for lasing. The optical cavityaxis of the laser diode 910 is oriented perpendicular to the directionof current flow, defining an edge-emitting device, so that the radiation909 emerges from the edge of the device 910 rather than from a topsurface thereof. The devices 910 may be assembled on a non-nativesubstrate 907, for example, by micro-transfer printing, electrostaticadhesion, or other mass transfer techniques. Respective mirror elements(illustrated as micro-steering mirrors 913) may also be assembled on thesubstrate 907 (for example, by micro-transfer printing, electrostaticadhesion, or other mass transfer techniques), and oriented relative tothe optical cavity axis of a laser diode 910 that is to be providedadjacent thereto, such that the radiation 909 from the laser diode 910is reflected and ultimately emitted in a direction perpendicular to thesubstrate 907.

The substrate 907 may be rigid in some embodiments, or may be flexiblein other embodiments, and electrically conductive thin-filminterconnects may be formed to electrically connect respective contactsof the laser diodes 910 in series and/or parallel configurations, atspacings similar to those described with reference to the arrays 300 a,300 b, and/or 600 herein. Likewise, as described above with reference tothe examples of FIGS. 6A-6C, the array 900 may include other types ofdevices and/or devices formed from different materials (e.g., powercapacitors, FETs, micro-lens arrays, etc.) integrated with the laserdiodes 910 on the substrate 907 at the spacings described herein.

Further embodiments described herein are directed to emitter arraysincluding beam shaping structures that can be configured to outputarbitrary distributions of light intensity as a function of field ofview angle using light that originates from multiple discrete laserdiodes of the array. In some embodiments, respective laser diodes of thearray are arranged on a surface of a non-native substrate with differentrelative orientations, such that the coherent light emission from therespective laser diodes is output in different directions (e.g.,corresponding to azimuth or elevation angles) based on the differentorientations. Beam shaping structures in accordance with embodimentsdescribed herein may generate incoherent output light. That is, whilethe respective light emissions from the individual laser diodes arecoherent, the light output beam from the array includes a combination orsuperposition of the respective emissions that may be incoherent, as thephase of the light emission from one of the laser diodes can beindependent of that from another. For example, embodiments describedherein may include widening the horizontal and/or vertical field ofview, and/or may provide local maxima or minima of intensity in specificdirections. In some embodiments, a micro-transfer printing process (orother micro-assembly process) may be used to arrange the individuallaser diodes on the non-native substrate with different relativeorientations. In contrast, laser diodes on a native substrate may bedefined with fixed or uniform orientations relative to one another.

Some advantages of incoherent superposition of respective laser diodeemissions as described herein may include an absence or lack of specklepatterns that may be caused by interference of the monochromatic lightemissions from the respective laser diodes of the array. Some LIDARapplication detection schemes may include incoherent/direct energydetection (which may measure amplitude changes of the reflected light),or coherent detection (which may measure Doppler shifts, or changes inphase of the reflected light). Although described primarily withreference to embodiments in which the laser diodes are implemented assurface-emitting laser diodes (such as the VCSELs 200 of FIGS. 2A-2C),it will be understood that edge-emitting laser diodes (such as theedge-emitting laser diodes 910 and mirror structures 913 of FIG. 9) maybe also be used in addition to or instead of the illustrated VCSELs 200in distributed VCSEL arrays 300 with the beam shaping structuresaccording to embodiments described herein, as shown for example in FIGS.10A-15E.

FIG. 10A is a perspective view illustrating a distributed emitter array1000 including laser diodes (illustrated as VCSELs 200) on a curvedsubstrate 1007 in accordance with some embodiments described herein. Thecurvature of the substrate 1007 provides the respective VCSELs 200 ofthe array 1000 with different orientations relative to one another, suchthat their respective lasing apertures, optical axes (210, 208 in FIG.2B), and coherent light emission are oriented in different directions toprovide incoherent output beam 1009. The curvature may be implementedusing a flexible substrate, such as the substrate 307 b of FIG. 3B. Someexample materials for the substrate 1007 that may have characteristicssufficient for the curvature or other deformation described withreference to FIGS. 10A-10D may include (but are not limited to) willowglass, thin zirconia (ZrO₂) ceramics, thin alumina (Al₂O₃) ceramics,silicon (Si), metals (aluminum, copper, etc.), and/orplastics/acrylates.

As shown in FIG. 10A, curvature of the substrate 1007 may be controlledin accordance with embodiments described herein such that the outputbeam 1009 provides a desired uniform or non-uniform angular powerdistribution, also referred to herein as an intensity distribution(energy per unit area) or photon flux distribution (photons per unitarea). The curvature of the substrate 1007 may or may not be constantradius, and can thereby be designed or otherwise selected to provide thedesired angular power distribution. For example, the substrate 1007 maydefine a cylindrical, acylindrical, spherical, or aspherical curve whosenormal surfaces provide the distribution of relative amounts of power inthe output beam 1009. An example non-uniform angular power distribution1003 of the beam 1009 that may be output from the array 1000 is shown inFIG. 10B. Although illustrated in FIG. 10B with reference to the azimuthangle θ, it will be understood that the non-uniform angular powerdistribution 1003 may correspond to an azimuth or elevation angle,depending on the axis of curvature of the substrate 1007.

To determine the curvature corresponding to a desired photon fluxdistribution, such as the angular power distribution 1003 shown in FIG.10B, line segments may be defined between control points. The linesegments may have a length that is proportional to the relative amountof power at the angle normal to that segment. A spline may be fitthrough the control points to determine or otherwise define a profile1004, as shown for example in the graph of FIG. 10C. The determinedprofile 1004 may define an aspherical or acylindrical curve whose normalsurfaces provide required distribution of relative amounts of power1003, as shown for example in FIG. 10B. The flexible substrate 1007 maythereby be bent or deformed based on the determined profile 1004, asshown for example in FIG. 10A. Additionally, the VCSELs 200 may bearranged on the non-native substrate 1007 at different and/ornon-uniform pitches to aid in providing a desired far-field output lightpattern 1009.

In some embodiments, the curvature of the substrate 1007 may bedynamically altered by mechanical or electro-mechanical actuation. Forexample, as shown in FIG. 10A, one or more controllable mandrels 1050may be configured to move in one or more planes of motion along thesubstrate 1007 responsive to control signals from a control circuit,such that the positioning of the mandrel(s) 1050 is configured to deformthe substrate 1007 to provide the desired curvature. In someembodiments, the mandrel(s) 1050 may be used to dynamically bend theflexible substrate 1007 to increase or decrease its curvature based onthe profile 1004 of FIG. 10C, to define a desired aperture shape andnon-uniform angular power distribution 1003 of FIG. 10B (e.g., morephotons output forward than at edges). The deformation of the substrate1007 can be performed dynamically in response to changing environmentalconditions, such that the field-of-view covered by the light emissionfrom the array 1000 may be varied. The mandrel(s) 1050 can also serve asa heat sink in some embodiments. Also, as mentioned above, a spatialdensity or concentration of VCSELs 200 at peripheral portions of thearray 1000 may be less than a concentration of VCSELs 200 at a centralportion of the array 1000 in some embodiments.

The curvatures of the array substrate 1007 shown and described withreference to FIGS. 10A-10C may be based on providing the output beam1009 with greater power distribution in particular direction(s) orangle(s) based on a distance and/or direction of desired operation, suchthat greater intensity may provide greater operating distance. In someembodiments, the greater operating distance may be desired to bestraight ahead (e.g., corresponding to a forward direction of travel),and the array 1000 may be deformed such that more of the laser diodesare oriented in the forward direction to provide the output beam 1009with greater photon flux distribution in the forward direction ascompared to directions that are peripheral to a forward direction oftravel.

However, in other embodiments described herein, it may be desirable toprovide the output beam 1009 with greater intensity toward the peripheryof the array 1000 (e.g., toward the left or right side of the array 1000rather than at the center), as shown for example, in the graph of FIG.10D. For instance, in some applications, one or more dedicatedsensors/sensor arrays may be used for the forward direction of travel(e.g., for longer range sensing along a road, which may correspond toprofile 1006), and the array 1000 may be an additional sensor array thatis configured to provide greater resolution in one or more directionsthat are peripheral to the forward direction of travel. As such, thearray 1000 may be bent according to the profiles 1008 a or 1008 b shownin FIG. 10D, which provide the output beam 1009 with greater angularpower distributions in directions peripheral to the straightahead/forward direction of the array 1000. The embodiments of FIGS.10A-10D have been described with reference to control of the curvatureof the substrate 1007 in a single dimension (shown as the “horizontal”direction) to provide varying angular power distributions over a fieldof view of up to about 180 degrees or more. However, it will beunderstood that curvature control in embodiments described herein is notlimited to a single dimension, and thus some embodiments may includemechanical and/or electro-mechanical actuators that are configured todeform the substrate 1007 in multiple dimensions (e.g., in bothhorizontal and vertical directions), thereby affecting both azimuth(horizontal divergence) and elevation (vertical divergence) of theoutput beam 1009. Moreover, in some embodiments an array of drivertransistors (such as the driver transistors 610 of FIGS. 6A-6C) may beassembled on the substrate 1007 and used to dynamically adjust orotherwise control the operation and/or emission power of individualVCSELs 200 or subsets of the VCSELs 200 in different areas of the array1000, for control of the angular power distribution alone or incombination with control of the curvature of the substrate 1007. Thedriver transistors 610 may also be used to sequentially activate columnsand/or rows of VCSELs 200 to provide electronic beam scanning over theangular power distribution defined by the curvature of the substrate1007. Furthermore, control of the curvature of the substrate 1007 may beused in conjunction with any of the lens arrays 1103 a-1103 c, 1203,1303 e, 1403 a-1403 c described herein with reference to FIGS. 11A-14C,as well as the tilted laser diode arrangements of FIGS. 15A-15F.

FIGS. 11A, 11B, and 11C are cross-sectional views illustrating exampledistributed emitter arrays with integrated optics 1100 a, 1100 b, and1100 c including shaped lenslet arrays that are configured forhigh-aspect ratio beam forming in accordance with some embodimentsdescribed herein. As shown in FIGS. 11A-11C, the arrays 1100 a, 1100 b,and 1100 c include optical elements in the form of lenslet array 1103 a,1103 b, and 1103 c, a plurality of laser diodes (illustrated as VCSELs200) assembled and electrically connected in strings to definerespective rows and/or columns of VCSEL arrays 300, and electricallyconductive interconnects 1113 that define the electrical connectionsbetween the VCSELs 200. The VCSELs 200 may be assembled on a non-nativesubstrate 1107 (in FIGS. 11A and 11C) or on a surface of the lensletarray 1103 b (in FIG. 11B) by micro-transfer printing, electrostaticadhesion, or other mass transfer techniques. For example, micro-transferprinting may achieve inter-VCSEL spacings of less than about 150micrometers (μm), or in some embodiments, less than about 100 μm, orless than about 50 μm, thereby increasing the active area fill factor ascompared to some conventional VCSEL arrays.

The substrate 1107 may be rigid or flexible. Some example materials forthe substrate 1107 that may have characteristics sufficient for thecurvature or other deformation described herein may include (but are notlimited to) willow glass, thin zirconia (ZrO₂) ceramics, thin alumina(Al₂O₃) ceramics, silicon (Si), metals (aluminum, copper, etc.), and/orplastics/acrylates.

The lenslet arrays 1103 a, 1103 c include a gap or interface 1180 inrespective emission paths 1190 between the respective lens elements 1103e (also referred to herein as lenslets) and corresponding ones of theVCSELs 200, which are aligned with the respective lens elements 1103 e.The interface 1180 may be defined by one or more spacer structures 1106that attach or otherwise integrate the lenslet arrays 1103 a, 1103 conto the surface of the substrate 1107 and separate the lenslet array1103 a from the surface of the substrate 1107 based on the focal lengthsof the lenslets 1103 e. In some embodiments, the spacer structures 1106may be formed of a transparent material, such as silicone, and may beimplemented as spaced apart spacer structures 1106 defining respectiveair gaps therebetween, or as a continuous transparent material layerthat fills the space between the VCSELs 200 and the lenslet arrays 1103a, 1103 c. In some embodiments, the lenslet arrays 1103 a, 1103 c may beformed of a glass lens element, or a silicone-on-glass lens element.

Light 1109 output from the respective VCSELs 200 may be collected bylenslets 1103 e of the lenslet arrays 1103 a, 1103 c, thus resulting inthe generation of multiple collimated light beams. Collimation can beachieved with micro-lens arrays 1103 a, 1103 b having the same pitch asthe VCSEL array 300, i.e. lenslet 1103 e per VCSEL 200. Curvature of thesubstrate 1107 and/or the lenslet arrays 1103 a, 1103 c may bedetermined and used as discussed above with reference to FIGS. 10A-10Dto provide the output light from the array at various angles, foremission of non-collimated beams (e.g., for horizontal and/or verticaldivergence). In some embodiments, the lens elements 1103 e may bedefined in the surface of the lenslet arrays 1103 a, 1103 b, 1103 c by amolding, casting, embossing, and/or etching process.

FIG. 11B illustrates an example distributed emitter array 1100 baccording to further embodiments described herein in which the VCSELs200 are integrated directly onto the surface of the lenslet array 1103b, such that the respective emission paths 1190 between the respectivelens elements 1103 e are free of gaps or air interfaces, providing amonolithic lenslet/emitter array structure. The thickness of the lensletarray 1103 b may be selected to effectively function as a spacerstructure for the entirety of the lenslet array 1103 b, to position theVCSELs 200 at a distance at or near the focal length of the individuallenslets 1103 e. As such, the surface of the lenslet array 1103 bfunctions as a non-native substrate. In some embodiments, the lensletarray 1103 b may be formed of a glass lens element on a silicone layer,or may be formed solely of silicone (e.g., molded silicone) or from alayer of gradient index material (which provide different refractiveindices by changing the loading fraction of high index nanoparticles).That is, the lenslet array 1103 b may provide the non-native substratefor the VCSELs 200.

FIGS. 11A and 11B illustrate example lenslet arrays 1103 a, 1103 bincluding similar plano-convex (PCX) lenses as the lenslet elements 1103e, which may provide collimated light output. However, in someembodiments as shown in FIG. 11C, the shapes of the lenslets 1103 e mayvary independently of one another in one or more directions, such thatthe output beams 1109 from the lens array 1103 c are non-collimated. Forexample, with reference to an X-Y plane defined by the surface of thesubstrate 1107, the shape of the lenslets 1103 e at ends of the array1103 c may differ from the lenslet 1103 e therebetween in theX-direction, to provide output light 1109 with differently shaped farfield patterns along the X-direction (which may correspond to ahorizontal divergence). The translationally symmetric design of thelenslets 1103 e shown in FIG. 11C can be used to spread the output light1109 in one direction (e.g., the X-direction), but not affect thespreading in another direction (e.g., the Y-direction). However, it willbe understood that the shapes of the lenslets 1103 e may likewise varyin the Y direction, in order to provide output light 1109 withdifferently shaped far field patterns along the X- and/or the Y-axes.More generally, the lens prescription can vary from lenslet to lenslet1103 e across the array 1103 c in order to realize a desired far fieldpattern. The lenslet arrays 1103 a, 1103 b, 1103 c may be formed of aflexible lens material such that the lenslet arrays 1103 a, 1103 b, 1103c can also be bent or deformed to provide a desired curvature profile,as discussed above with reference to FIGS. 10A-10D, such that the outputlight 1109 from the arrays 1100 a, 1100 b may provide a desired angularpower distribution.

Although illustrated in FIGS. 11A-11C as single-stage designs, in someembodiments, the arrays 1100 a, 1100 b, 1100 c may include multi-stageoptics, with the illustrated arrays of optics 1103 a, 1103 b, 1103 caligned with and configured to receive light 1109 from an array ofprimary optics, such as the ball lenses shown in FIGS. 12A-12B. Such amulti-stage design can provide greater flexibility and performance, forexample, by using one stage of the multi-stage optics to providehorizontal divergence of the output light emission, and the next stageto provide vertical divergence of the output light emission, or viceversa.

FIGS. 12A and 12B are cross-sectional views illustrating exampledistributed emitter arrays with integrated optics 1200 a and 1200 b,including a self-aligned ball lens arrays 1203 that are configured forwide field-of-view beam forming in accordance with some embodimentsdescribed herein. Optical alignment of a ball lens to a VCSEL mayconventionally utilize active alignment, whereby the ball lens may bemoved in x, y, and z space while monitoring the far field pattern foroptimal coupling. This alignment process can be slow and expensive,particularly for large arrays of VCSELs that may requiretens/hundreds/thousands of ball lenses to collimate each laser beamemitted by the array.

Some embodiments described herein may achieve optical alignment of aball lens to a VCSEL using a self-aligned method, for example, usingalignment features (such as photolithographically-defined features) toallow respective ball lens elements 1203 e to self-align in x, y, and zspace. For example, as shown in FIGS. 12A and 12B, the arrays 1200 a and1200 b include optical elements in the form of ball lens arrays 1203, aplurality of laser diodes (illustrated as VCSELs 200) assembled andelectrically connected in strings to define respective rows and/orcolumns of emitter arrays 300, and electrically conductive interconnects1213 that define the electrical connections between the VCSELs 200. TheVCSELs 200 may be assembled on a non-native substrate 1207 a and 1207 bby micro-transfer printing, electrostatic adhesion, or other masstransfer techniques. The substrates 1207 a, 1207 b may be rigid orflexible, and may be formed from (but are not limited to) willow glass,thin zirconia (ZrO₂) ceramics, thin alumina (Al₂O₃) ceramics, silicon(Si), metals (aluminum, copper, etc.), and/or plastics/acrylates.

In the embodiment of FIG. 12B, the VCSELs 200 are formed on a backsideof the substrate 1207 b, which is formed of a material that istransparent to the wavelength range of the light 1209 emitted by theVCSELs 200. The substrate 1207 b may have a thickness and/or refractiveproperties that affect the optical path of the light output from theVCSELs 200 such that the lens array 1203 is provided at a desired focaldistance. Advantages of this configuration 1200 b (also referred toherein as back- or bottom-illumination) may include protection orisolation of the VCSELs 200 from processing conditions (e.g.,temperature, chemicals, etc.) used in fabricating the optics 1203. Thethickness of the substrate 1207 b may also aid in collimation of thelight output 1209, for example, as the optical path through the opposingsurfaces of the substrate 1207 b may provide additional refraction priorto entering the lens elements 1203 e. In further embodiments, thesubstrate 1207 b may have a thickness and/or refractive properties thatmay be sufficient to provide collimation of the light output 1209without the need for further lens elements 1203 e, that is, such thatthe lens array 1203 need not be present.

In FIGS. 12A and 12B, the non-native substrates 1207 a and 1207 bfurther include alignment features 1206 a and 1206 b on surfacesthereof. The spacing between pairs of the alignment features 1206 a,1206 b may be sized and configured to suspend respective ball lenselements 1203 e over respective VCSELs 200, such that a respectiveoptical axis of each ball lens element 1203 e is aligned with theoptical axis defined by a lasing aperture of an underlying VCSEL 200.

In some embodiments, the ball lens elements 1203 e may each have arespective diameter of about 250 μm or less, for compatibility with thedimensions of VCSEL-based VCSEL arrays 300 as described herein. Toachieve precise alignment between the optical axes of such small balllens elements 1203 and the VCSELs 200 described herein, the alignmentfeatures 1206 a and 1206 b may be photolithographically-defined in someembodiments. For example, the alignment features 1206 a and 1206 b maybe formed from a dry-film resist layer that is photolithographicallypatterned to define holes therein, where the holes are sized and shapedto align the optical axes of ball lens elements 1203 e of apredetermined diameter with the optical axis defined by the respectiveapertures of the VCSELs 200. It will be understood, however, that someapplications (e.g., flash LIDAR) may be tolerant of missing or imperfectindividual lens 1203 e/VCSEL 200 optical axis alignment among thehundreds or thousands of lenses 1203 e/VCSELs 200 in the arrays 1200 a,1200 b, and that other materials may be used to define the alignmentfeatures 1206 a and 1206 b.

The alignment features 1206 a and 1206 b may also be sized to definesufficient gaps between each ball lens element 1203 e and an underlyingVCSEL 200 to provide desired collimation of the light 1209 output fromthe underlying VCSEL 200. Different materials may be selected for thealignment features 1206 a and 1206 b based on the size of the desiredgaps (and the corresponding heights of the alignment features 1206 a and1206 b), alone or in combination with additional features for supportingthe ball lenses. In some embodiments, a transparent material may fillthe gap between a lens element 1203 e and the underlying VCSEL 200 (orlikewise, the gap between lens arrays 1103 a, 1103 c and VCSELs 200).For example, the gap may be air, silicone, or another material that istransparent to the wavelength range of the light 1209 emitted by theVCSELs 200.

Some embodiments described herein may be of greater benefit inapplications including very large arrays 1200 a, 1200 b on ultra-smalldies, with ball lenses 1203 e with diameters smaller than about 250 μm,for example in LIDAR applications. In some embodiments,micro-transfer-printing (MTP) may be used to print the array 1203 ofpre-aligned ball lenses 1203 e onto the VCSEL array 300. In furtherembodiments, BGA technology may be used for pre-alignment, where theball lenses 1203 e can be pre-aligned by pouring them onto a grid thathas been photolithographically produced to define the ball lens array1203, and the MTP stamp may pick-up the ball lens array 1203 from thepre-alignment grid and deposit the ball lens array 1203 on top of theVCSEL array 300 such that the ball lenses 1203 e are aligned by thealignment features 1206 a, 1206 b. In some embodiments, the ball lensarrays 1203 of FIGS. 12A and 12B may be used in combination with anoverlying lens array, such as the Fresnel lens 1403 of FIGS. 14A-14C, inorder to further modify the field of view (e.g., the vertical divergenceof the light output 1209).

FIGS. 13A and 13B are cross-sectional views and FIG. 13C is aperspective view illustrating example distributed emitter arrays withintegrated optics 1300 a, 1300 b, and 1300 c including offset ball lensarrays for beam forming in accordance with some embodiments describedherein. As shown in FIGS. 13A-13C, the arrays 1300 a, 1300 b, 1300 cinclude optical elements in the form of ball lens arrays, a plurality oflaser diodes (illustrated as VCSELs 200) assembled and electricallyconnected in strings to define respective rows and/or columns of VCSELarrays 300, and electrically conductive interconnects 1313 that definethe electrical connections between the VCSELs 200. The VCSELs 200 may beassembled on non-native substrates 1307 a, 1307 b, 1307 c bymicro-transfer printing, electrostatic adhesion, or other mass transfertechniques. The substrates 1307 a, 1307 b, 1307 c may be rigid in someembodiments, or flexible in other embodiments.

As shown in FIGS. 13A-13C, each lens element 1303 e of the lens array issuspended over multiple VCSELs 200, such that the direction of lightemission from each VCSEL 200 is offset relative to the optical axis ofthe respective lens element 1303 e. For example, as shown in theenlarged cross-sections of FIGS. 13A and 13B, the non-native substrates1307 a and 1307 b include alignment features 1306 a and 1306 b onsurfaces thereof, where the spacing between pairs of the alignmentfeatures 1306 a, 1306 b is sized and configured to suspend respectiveball lens elements 1303 e over a 2×−2 sub-array of VCSELs 200 such thatthe optical axis of each ball lens element 1303 e is misaligned with therespective optical axes defined by the lasing apertures of theunderlying VCSEL 200s, and the lens element 1303 e diffracts the lightemission from the underlying VCSELs 200 into non-collimated beams 1309.

The examples of FIGS. 13A-13C are illustrated with reference to beams1309 having increased horizontal and vertical divergence, as comparedwith the aligned lens elements 1203 e of FIGS. 12A-12B. In someembodiments, the substrates 1307 a, 1307 b, 1307 c may be curved toprovide further horizontal and/or vertical divergence. For example, thesubstrates 1307 a, 1307 b, 1307 c may be formed from (but are notlimited to) willow glass, thin zirconia (ZrO₂) ceramics, thin alumina(Al₂O₃) ceramics, silicon (Si), metals (aluminum, copper, etc.), and/orplastics/acrylates. In the embodiment of FIG. 13B, the substrate 1307 bis formed of a material that is transparent to the wavelength range ofthe light 1309 emitted by the VCSELs 200. The substrate 1307 b may havea thickness and/or refractive properties that affect the optical path ofthe light output from the VCSELs 200 such that the lens elements 1303 eare provided at a desired focal distance.

In the example of FIG. 13C, the array 1300 c further includes integrateddriver transistors 1310 that are assembled on the substrate 1307 cadjacent to one or more of the VCSELs 200, for example, using amicro-transfer printing (MTP) process. For example, the array 1300 cincludes a plurality of 2×−2 sub-arrays of monolithic VCSELs 200 thatare electrically connected in series (or anode-to-cathode) to definecolumns or other subsets of the array 1300 c. The array 1300 c furtherincludes an array of driver transistors 1310, with each driver 1310electrically connected in series with a respective column (or othersubset) of 2×−2 sub-arrays of VCSELs 200. The driver transistors 1310may also be used to sequentially activate columns and/or rows of VCSELs200 to provide electronic beam scanning. The integration of the array ofdriver transistors 1310 with the sub-arrays of VCSELs 200 may otherwisebe similar to the array 600 of FIGS. 6A-6C, and thus, furtherdescription will not be provided.

In some embodiments, the ball lens arrays of FIGS. 13A-13C may be usedin combination with an overlying lens array, such as the Fresnel lens1403 of FIGS. 14A-14C, in order to further modify the field of view(e.g., the vertical divergence of the light output 1309).

FIGS. 14A, 14B, and 14C are cross-sectional views illustrating exampledistributed emitter arrays with integrated optics 1400 a, 1400 b, and1400 c including lens arrays having primary and/or secondary lenselements that are configured for multi-direction beam forming inaccordance with some embodiments described herein. The array 1400 a ofFIG. 14A includes a plurality of laser diodes (illustrated as VCSELs200) assembled and electrically connected in strings to definerespective rows and/or columns of VCSEL arrays 300, and electricallyconductive interconnects 1413 that define the electrical connectionsbetween the VCSELs 200. The VCSELs 200 may be assembled on a non-nativesubstrate 1407 by micro-transfer printing, electrostatic adhesion, orother mass transfer techniques. The substrate 1407 may be rigid orflexible, and may be formed from (but is not limited to) willow glass,thin zirconia (ZrO₂) ceramics, thin alumina (Al₂O₃) ceramics, silicon(Si), metals (aluminum, copper, etc.), and/or plastics/acrylates.

The embodiment of FIG. 14A includes a primary lens array 1403 aincluding respective lens elements 1403 e that are suspended overrespective VCSELs 200 by alignment features 1406 that are sized, spaced,and configured to align a respective optical axis of each lens element1403 e with the optical axis defined by a lasing aperture of anunderlying VCSEL 200. The lens elements 1403 e may be ball lenses (suchas spherical lenses) in some embodiments, or may be cylindrical lensesin some embodiments. The lens elements 1403 e of the primary lens array1403 a may be configured to increase azimuth (horizontal divergence) ofthe output beam 1409 from the array 1400 a.

Still referring to FIG. 14A, the array 1400 a further includes asecondary lens array 1404 a (illustrated as a Fresnel lens). Thesecondary lens array 1404 a is configured to increase elevation(vertical divergence) of the output beam 1409, while substantiallymaintaining horizontal beam divergence (e.g., within <1 degree percolumn). In the example of FIG. 14A, the secondary lens array 1404 a isimplemented as a thin flexible linear Fresnel lens cover (includingrespective Fresnel lenslets 1404 e) that is provided over the VCSELarray 300 and the primary lens array 1403 a thereon, in order to divergethe emitted light from each VCSEL 200 by about 15 degrees to about 26degrees vertically. In embodiments where the substrate 1407 is formed ofa flexible material, the array 1400 a may also be bent to achieve anoverall horizontal Field-of-View (FoV) of up to about 150 degrees ormore. However, the secondary lens element 1404 a is not limited to aFresnel lens; for example, the secondary lens element 1404 a may beimplemented by a flexible diffusing film in some embodiments.

As such, in some embodiments, light from each VCSEL 200 may becollimated to about 0.1 degree per column horizontally using arespective ball lens 1403 e. In other embodiments, the light from eachcolumn of VCSELs 200 of the array 300 may be collimated using acylindrical lens element 1403 e to provide about 0.1 degree horizontalcollimation. That is, the array 1400 a of FIG. 14A utilizes acombination of primary lens elements (e.g., ball or cylindrical lenses1403 e) and secondary lens elements (e.g., Fresnel lens 1404 a) tocontrol horizontal and vertical divergence of the output laser beams1409 from respective VCSELs 200.

The alignment features 1406 used to self-align the lens elements 1403 e(whether ball or cylindrical) may be photolithographically defined, forexample, from a dry-film resist layer that is patterned to define holes(for the ball lenses 1403 e) or trenches (for the cylindrical lenses1403 e) therein. However, in other embodiments, the primary lens array1403 a may be omitted; for example, the secondary lens array 1404 a mayprovide vertical divergence of the output beam 1409, with horizontaldivergence provided by the curvature of the substrate 1407.

In the embodiment of FIG. 14A, the secondary lens array 1404 a includesrespective Fresnel lenslets 1404 e, each of which has an optical axisthat is aligned with those of the underling primary lens element 1403 eand VCSEL 200. FIG. 14B illustrates alternate configuration of adistributed emitter array with integrated optics 1400 b, which includesa large-area Fresnel lens array 1404 b overlying the entire array 300 ofVCSELs 200. That is, each VCSEL 200 is positioned beneath a differentregion of a single Fresnel aperture 1404 b. In the example of FIG. 14B,the lens elements 1403 e are omitted. As such, the large-area Fresnellens array 1404 b may provide vertical divergence of the output beam1409, with horizontal divergence provided by curvature of the substrate1407. The lens 1404 b may be flexible (e.g., plastic) Fresnel lens insome embodiments. Also, as mentioned above, the lens array 1404 b is notlimited to a Fresnel lens array, but may be implemented by a flexiblediffusing film in some embodiments.

A further embodiment of a distributed emitter array with integratedoptics 1400 c is shown in FIG. 14C, in which multiple layers of lensarrays 1403 c, 1404 c (illustrated as respective large-area Fresnellenses) are used in sequence in order to realize a desired far fieldpattern of the output beam 1409. In the example of FIG. 14C, the lensarray 1403 c is used to affect the angle of laser emission in onedimension (e.g., horizontal divergence in an X-direction along thesurface of the substrate 1407), while the lens array 1404 c is used toaffect the angle of laser emission in another dimension (e.g., verticaldivergence in a Y-direction along the surface of the substrate 1407), orvice versa. That is, the arrays 1400 a, 1400 c include a stacked lensarray structure whereby a first lens element 1403 a, 1403 c alters thefar field pattern of the output beam 1409 in a first dimension, while asecond lens element 1404 a, 1404 c alters the far field pattern of theoutput beam 1409 in a second dimension.

While illustrated in FIGS. 14A-14C with reference to embodiments inwhich the lens arrays 1403 c, 1404 a- c and VCSELs 200 are stacked on asurface of a substrate 1407, it will be understood that the substrate1407 may be transparent to the wavelength range of the light output fromthe VCSELs 200 in some embodiments, and the VCSELs 200 may be arrangedto transmit light through the transparent substrate (as shown in FIGS.12B and 13B) to the lens arrays 1403 c, 1404 a-c.

FIGS. 14A-14C are also illustrated primarily with reference to arrays ofFresnel lenses 1404 a, 1404 b, 1403 c, 1404 c, which may be formed frommaterials having sufficient physical flexibility for integration withflexible substrate 1407 implementations, thereby allowing for adjustmentof the curvature of the arrays 1400 a, 1400 b, 1400 c in a mannersimilar to those described above with reference to FIGS. 10A-10D.However, it will be understood that embodiments described herein are notlimited to such Fresnel lens arrays, and other flexible optical elementsand/or micro-structured lenslets may be used to affect the far fieldpattern of the output beam 1409 by scattering the light from the laserdiodes 200. For example, one or more of the lens arrays 1404 a, 1404 b,1403 c, 1404 c may be implemented by incoherent micro-optical scatteringdiffusers, such as those made by Brightview technologies and Luminit.Embodiments described herein may utilize these and/or other opticalelements for the modification of far field patterns of VCSEL arrays, forexample, in LIDAR applications.

Results illustrating the output beams provided by flexible opticaldiffusers on VCSEL arrays to modify FoV are illustrated in FIGS. 14D, ascompared to the absence of such optical diffusers in FIG. 14E. Thearrangement of these optical diffusers may be similar to thearrangements of FIGS. 14A-14C, with the optical diffusers replacing theillustrated Fresnel lens arrays 1404 a, 1404 b, 1403 c, 1404 c. As shownin FIG. 14D, the optical diffuser may significantly widen the elevationcoverage, shown by the increase in the full width at half maximum (FWHM)of the elevation beam profile 1409 e′ of the output beam 1409 ascompared to the elevation beam profile 1409 e shown in FIG. 14E. As alsoshown in FIG. 14D, the FWHM of the azimuth beam profile 1409 a′ of theoutput beam 1409 is relatively unchanged by the optical diffuser, shownby the similar FWHM of the azimuth beam profile 1409 a in FIG. 14E.

That is, although illustrated in FIGS. 14A-14C with respect toFresnel-type lens elements to provide vertical divergence, it will beunderstood that other types of lens elements may be integrated over asurface of the emitter array 300 to provide vertical beam divergence, incombination with a lens array that is configured to provide horizontalbeam divergence, or alone (e.g., where the curvature of the substrate1407 provides horizontal beam divergence). More generally, theembodiments of FIGS. 14A-14C may use any combination of curvature of thesubstrate 1407, primary lens elements 1403 a, 1403 c, and secondary lenselements 1404 a, 1404 b, 1404 c to provide horizontal and/or verticaldivergence of the output beam 1409.

FIGS. 15A, 15B, 15C, 15E, and 15F are cross-sectional views illustratingportions of example distributed emitter arrays 1500 a, 1500 b, 1500 c,1500 e, and 1500 f including tilted laser diodes for lensless beamforming in accordance with some embodiments described herein. FIG. 15Dis a plan view illustrating the portion of the array 1500 c of FIG. 15C.

As shown in FIGS. 15A-15E, laser diodes (illustrated as VCSEL chiplets200) are assembled on a rigid or flexible non-native target substrate1507 by micro-transfer printing, electrostatic adhesion, or other masstransfer techniques. The VCSEL chiplets 200 may be electricallyconnected in strings to define respective rows and/or columns of emitterarrays by electrically conductive interconnects to anode and cathodecontacts 211, 212 that are smaller than their respective lasingapertures 210 in at least one dimension, as shown in FIGS. 2A and 2B.The electrically conductive interconnects may be formed by patterning anelectrically conductive film after providing the VCSEL chiplets 200 onthe substrate 1507, for example, using conventional photolithographytechniques, rather than incorporating wire bonds, ribbons, cables, orleads. In some embodiments, a stamp having a planar or a sawtooth-shapedsurface may be used to pick-up the VCSEL chiplets 200 from a sourcesubstrate or wafer (e.g., in a manner similar to that shown in FIGS.4A-4F and 4A′-4G′), and print the VCSEL chiplets 200 onto the targetsubstrate 1507.

Still referring to FIGS. 15A-15E, the VCSEL chiplets 200 may bedifferently oriented by one or more physical features 1506 a-1506 e onthe substrate 1507, such that the optical axes defined by theirrespective lasing apertures 210 have respective tilt angles θ relativeto a direction that is normal to a surface of the substrate 1507. Asshown in FIG. 15E, in some embodiments the substrate 1507 may include apatterned or structured surface 1506 e such that the VCSEL chiplets 200are angled to provide the respective tilt angles θ as-deposited on thesurface 1506 e. As shown in FIGS. 15A-15D, pairs of rail- or bar-shapedfeatures 1506 a and 1506 b of different heights H_(A) and H_(B) may bedeposited on the substrate 1507 and spaced apart at distances sufficientto angle the VCSEL chiplets 200 to provide the respective tilt angles θwhen deposited thereon. An underfill material, such as an adhesivelayer, may be provided between each VCSCEL 200 and the underlyingsubstrate features 1506 a-1506 e to improve adhesion, electricalcontact, and/or pull the VCSEL 200 toward the surface of the non-nativesubstrate 1507 in some embodiments.

The VCSEL chiplets 200 may be printed such that their respective lasingapertures 210 point away from the substrate 1507, as shown in FIGS. 15Aand 15C-15E, thereby directing output beam 1509 away from the substrate1507. Alternatively, as shown in FIG. 15B, the substrate 1507 may betransparent, and the VCSEL chiplets 200 may be printed upside-down suchthat their lasing apertures 210 point toward the substrate 1507, andsuch that the lasing aperture 210 directs light between the bar features1506 a, 1506 b to provide the output beam 1509 through the substrate1509, also referred to herein as bottom-illumination. In somebottom-illumination embodiments, the space between the VCSEL chiplets200 and the substrate 1507 may be underfilled with a transparentmaterial, for example silicone, to provide refractive index-matching.

In FIGS. 15A-15D, the VCSEL chiplets 200 are deposited onto the pairs ofrail- or bar-shaped features 1506 a and 1506 b having different heightsH_(A) and H_(B) to define the respective tilt angles (θ) relative to thesurface of the substrate 1507. The tilt angles θ can be varied for eachVCSEL chiplet 200 by selecting the pitch (P) and/or relative differencesin height (H_(A) and H_(B)) of the bar features 1506 a and 1506 b. Thatis, one or more pairs of bar features 1506 a and 1506 b may havedifferent relative heights and/or pitches as compared to other pairs ofbar features 1506 a and 1506 b on the same target substrate 1507. Forexample, as shown in FIGS. 15C and 15D, platform features 1506 c can beprovided between at least one of the bar features 1506 a and 1506 b andthe surface of the substrate 1507 to increase relative heightdifferences therebetween. In some embodiments, the bar features 1506 a,1506 b may be elements of equal height, with the height differenceprovided by stacking bar feature 1506 b on platform feature 1506 c. Thesurface of the target substrate 1507 may be patterned or otherwisedefined to include recess features 1506 d, which may be sized andoriented to accommodate a lower corner of the tilted VCSELs 200. Thefeatures 1506 a-1506 c can be formed from conductive and/ornon-conductive materials, using semiconductor processes. For example,the bar features 1506 a and 1506 b may be line features that arepatterned in different thicknesses of metal or photoresist. In someembodiments, multiple layers of materials can be used to build-upthicknesses of bar features 1506 a and 1506 b. In some embodiments, thefeatures 1506 a, 1506 b, 1506 c may be micro-transfer printed on thesurface of the substrate 1507. The VCSELs 200 that are printed orotherwise deposited onto these varying height/pitch bar feature pairs1506 a and 1506 b may thus define an array of discrete VCSELs 200 withvarying orientations and emission angles, providing wider fields ofview/illumination.

Although discussed primarily with reference to tilt orientations toprovide divergence in one dimension (for example, elevationangle/vertical divergence, with azimuth angle/horizontal divergence tobe provided by curvature of a flexible substrate 1507), it will beunderstood that the features 1506 a-1506 e may be oriented at differentrespective angles (rather than in a grid) such that each tilted VCSEL200 has both a horizontal divergence component and a vertical divergencecomponent, either of which can be further increased by curvature of thesubstrate 1507 along a corresponding dimension.

Also, although illustrated in FIGS. 15A-15E with reference to VCSELchiplets 200, it will be understood that tilted emitter structures inaccordance with embodiments described herein can be implemented usingedge-emitting laser diodes 910, as shown in the example distributedemitter array 1500 f of FIG. 15F. In FIG. 15F, the edge-emitting laserdiode 910 is printed or otherwise deposited on a planar portion of thesurface of the substrate 1507, and a micro-steering mirror structure 913is printed or otherwise deposited on the bar features 1506 a and 1506 bat an angle such that the output beam 1509 is reflected to provide therespective tilt angle θ; however, it will be understood that either orboth of the laser diode 910 and the mirror structure 913 may bedeposited on any combination of physical features 1506 a-1506 e on thesubstrate 1507 to provide desired respective tilt angles θ.

The present invention has been described above with reference to theaccompanying drawings, in which embodiments of the invention are shown.However, this invention should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, the thickness of layers and regions are exaggerated forclarity. Like numbers refer to like elements throughout.

It will be understood that when an element is referred to as being “on,”“connected,” or “coupled” to another element, it can be directly on,connected, or coupled to the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly on,” “directly connected,” or “directly coupled” to anotherelement, there are no intervening elements present.

It will also be understood that, although the terms first, second, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower”, can therefore, encompasses both an orientation of “lower” and“upper,” depending of the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

The terminology used in the description of the invention herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of the invention. As used in the description ofthe invention and the appended claims, the singular forms “a”, “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will also be understood that theterm “and/or” as used herein refers to and encompasses any and allpossible combinations of one or more of the associated listed items. Itwill be further understood that the terms “include,” “including,”“comprises,” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Embodiments of the invention are described herein with reference toillustrations that are schematic illustrations of idealized embodiments(and intermediate structures) of the invention. As such, variations fromthe shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are to be expected. Thus,the regions illustrated in the figures are schematic in nature and theirshapes are not intended to illustrate the actual shape of a region of adevice and are not intended to limit the scope of the invention.

Unless otherwise defined, all terms used in disclosing embodiments ofthe invention, including technical and scientific terms, have the samemeaning as commonly understood by one of ordinary skill in the art towhich this invention belongs, and are not necessarily limited to thespecific definitions known at the time of the present invention beingdescribed. Accordingly, these terms can include equivalent terms thatare created after such time. It will be further understood that terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe present specification and in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference in their entireties.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of allcombinations and subcombinations of the embodiments of the presentinvention described herein, and of the manner and process of making andusing them, and shall support claims to any such combination orsubcombination.

Although the invention has been described herein with reference tovarious embodiments, it will be appreciated that further variations andmodifications may be made within the scope and spirit of the principlesof the invention. Although specific terms are employed, they are used ina generic and descriptive sense only and not for purposes of limitation,the scope of embodiments of the present invention being set forth in thefollowing claims.

1. A laser array, comprising: a plurality of laser diodes arranged andelectrically connected to one another on a surface of a non-nativesubstrate, wherein respective laser diodes of the plurality of laserdiodes have different orientations relative to one another, wherein therespective laser diodes are configured to provide coherent lightemission in different directions, and wherein the laser array isconfigured to emit an output beam comprising the coherent light emissionfrom the respective laser diodes.
 2. The laser array of claim 1, whereinthe laser array comprises a LIDAR array, and wherein the output beamcomprises incoherent light having a non-uniform intensity distributionover a field of view of the laser array.
 3. The laser array of claim 1,wherein the non-native substrate comprises a curvature that provides thedifferent orientations of the respective laser diodes.
 4. The laserarray of claim 3, wherein the non-native substrate is a flexiblesubstrate that is bent to define the curvature.
 5. The laser array ofclaim 4, wherein the non-uniform intensity distribution is controllableresponsive to a control signal to alter the curvature of the flexiblesubstrate, and/or responsive to power supplied to the respective laserdiodes via selective addressing.
 6. The laser array of claim 4, whereinthe flexible substrate is supported by at least one mandrel element thatis configured for movement in one or more directions responsive to thecontrol signal, and wherein the movement of the at least one mandrelelement alters the curvature of the flexible substrate.
 7. The laserarray of claim 1, wherein the surface comprises a back surface of thenon-native substrate, wherein the respective laser diodes are arrangedto provide the coherent light emission through the non-native substrate,and wherein the non-native substrate comprises a material that istransparent to and is configured to at least partially collimate thecoherent light emission.
 8. The laser array of claim 1, whereinrespective features on the surface of the non-native substrate providethe different orientations of at least one of the respective laserdiodes.
 9. The laser array of claim 8, wherein the respective featurescomprise unequal-height features and/or recesses that are sized andspaced to provide the different orientations of the respective laserdiodes.
 10. The laser array of claim 8, wherein the respective featurescomprise respective patterned surfaces of the non-native substrate. 11.The laser array of claim 1, wherein the laser array is configured toemit the output beam without a refractive optical element on theplurality of laser diodes.
 12. The laser array of claim 1, furthercomprising a lens that is attached to the non-native substrate and isconfigured to alter a divergence of the output beam in at least onedimension.
 13. The laser array of claim 12, wherein the lens comprises aflexible material having a curvature corresponding to the curvature ofthe non-native substrate and/or corresponding to the differentorientations of the respective laser diodes.
 14. The laser array ofclaim 13, wherein the lens comprises a primary lens that is configuredto alter the divergence of the output beam in a first direction, and asecondary lens positioned to receive output beam from the primary lensand alter the divergence thereof in a second direction.
 15. The laserarray of any of claim 14, wherein the lens comprises at least one of aFresnel lens, a plurality of shaped lenslets, an optical diffuser, or aplurality of ball lenses.
 16. The laser array of claim 15, whereinrespective ball lenses of the plurality of ball lenses are suspendedover respective subsets of the plurality of laser diodes, and whereinoptical axes of the respective ball lenses are offset with respect tooptical axes defined by respective lasing apertures of the respectivesubsets of the plurality of laser diodes.
 17. The laser array of claim12, wherein a subset of the plurality of laser diodes defines a columnof the laser array, and wherein the lens comprises a respectivecylindrical lens that has a specific orientation relative to the column.18. The laser array of claim 1, wherein the respective laser diodescomprise a residual tether portion and/or a relief feature at aperiphery thereof, wherein a spacing between immediately adjacent laserdiodes of the plurality of laser diodes is less than about 500micrometers.
 19. The laser array of claim 1, wherein respective subsetsof the plurality of laser diodes are electrically connectedanode-to-cathode on the non-native substrate.
 20. The laser array ofclaim 1, wherein the respective laser diodes are surface-emittinglasers, wherein respective lasing apertures of the surface-emittinglasers define optical axes that are oriented in the differentdirections, respectively, and wherein respective electrical contacts tothe surface-emitting lasers are smaller than the respective lasingapertures thereof in at least one dimension.